Dibenzo[c,g]carbazole compound, light-emitting element, light-emitting device, display device, lighting device and electronic device

ABSTRACT

Provided is a novel compound which can be used for a transport layer or as a host material or a light-emitting material in a light-emitting element and with which a high-performance light-emitting element can be manufactured. A dibenzo[c,g]carbazole compound in which an aryl group having 14 to 30 carbon atoms and including at least anthracene is bonded to nitrogen of a dibenzo[c,g]carbazole derivative is synthesized. By use of the dibenzo[c,g]carbazole compound, a light-emitting element having very good characteristics can be obtained.

TECHNICAL FIELD

The present invention relates to a dibenzo[c,g]carbazole compound. Thepresent invention further relates to a light-emitting element, alight-emitting device, a display device, a lighting device, and anelectronic device each using the dibenzo[c,g]carbazole compound.

BACKGROUND ART

A display device using a light-emitting element (organic EL element) inwhich an organic compound is used as a light-emitting substance has beendeveloped rapidly as a next generation lighting device or display devicebecause it has advantages that such a light-emitting element can beformed to be thin and lightweight, has very high response speed forinput signals, and has low power consumption.

In an organic EL element, when a voltage is applied between electrodeswith a light-emitting layer interposed therebetween, electrons and holesinjected from the electrodes recombine to form an excited state, andwhen the excited state returns to a ground state, light emission isobtained. Since the wavelength of light emitted from a light-emittingsubstance is peculiar to the light-emitting substance, use of differenttypes of organic compounds for light-emitting substances makes itpossible to provide light-emitting elements which exhibit variouswavelengths, i.e., various colors.

Light emitted from a light-emitting substance is peculiar to thesubstance, as described above. However, important performances as alight-emitting element, such as lifetime and power consumption, are notonly dependent on the light-emitting substance but also greatlydependent on layers other than the light-emitting layer, an elementstructure, properties of a light-emitting substance and a host,compatibility between them, and the like. Thus, it is true that manykinds of light-emitting element materials are necessary for a growth inthis field. For the above-described reasons, light-emitting elementmaterials with a variety of molecular structures have been proposed(e.g., Patent Documents 1 to 3).

The substance named 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: CzPA) is one of materials which can be used as atransport material or a host material of a light-emitting layer in alight-emitting element. By using CzPA as a host material or anelectron-transport material, a light-emitting element which providesblue fluorescence and has very excellent characteristics in terms ofemission efficiency, driving voltage, and lifetime can be manufactured.

REFERENCES

-   [Patent Document 1] United States Published Patent Application No.    2008/0122344-   [Patent Document 2] PCT International Publication No. 2010/114264-   [Patent Document 3] PCT International Publication No. 2011/010842

DISCLOSURE OF INVENTION

Although many light-emitting element materials have been proposed sofar, it is very difficult to develop materials, like CzPA describedabove, with which it is possible to manufacture a light-emitting elementthat provides blue fluorescence and has the right combination ofimportant excellent characteristics in terms of emission efficiency,driving voltage, and lifetime.

Therefore, an object of one embodiment of the present invention is toprovide a novel compound which can be used for a transport layer or as ahost material or a light-emitting material in a light-emitting elementand with which a high-performance light-emitting element can bemanufactured.

Another object of one embodiment of the present invention is to providea light-emitting element having high emission efficiency which uses theabove novel compound. Another object of one embodiment of the presentinvention is to provide a light-emitting element having low drivingvoltage which uses the above novel compound. Another object of oneembodiment of the present invention is to provide a light-emittingelement having a long lifetime which uses the above novel compound.Another object of one embodiment of the present invention is to providea light-emitting element having favorable characteristics in terms ofemission efficiency, driving voltage, and lifetime which uses the abovenovel compound.

Another object of one embodiment of the present invention is to providea light-emitting device having low power consumption which uses alight-emitting element using the above novel compound. Another object ofone embodiment of the present invention is to provide a highly reliablelight-emitting device which uses a light-emitting element using theabove novel compound.

Another object of one embodiment of the present invention is to providea display device having low power consumption which uses alight-emitting element using the above novel compound. Another object ofone embodiment of the present invention is to provide a highly reliabledisplay device which uses a light-emitting element using the above novelcompound.

Another object of one embodiment of the present invention is to providea lighting device having low power consumption which uses alight-emitting element using the above novel compound. Another object ofone embodiment of the present invention is to provide a highly reliablelighting device which uses a light-emitting element using the abovenovel compound.

Another object of one embodiment of the present invention is to providean electronic device having low power consumption which uses alight-emitting element using the above novel compound. Another object ofone embodiment of the present invention is to provide a highly reliableelectronic device which uses a light-emitting element using the abovenovel compound.

Note that in one embodiment of the present invention, it is onlynecessary that at least one of the above-described objects should beachieved.

The present inventors have synthesized a dibenzo[c,g]carbazole compoundin which an aryl group including at least an anthracene skeleton isbonded to nitrogen at the 7-position of a dibenzo[c,g]carbazolederivative and have found that a light-emitting element having very goodcharacteristics can be easily provided by use of thedibenzo[c,g]carbazole compound.

Specifically, a structure of the present invention is a light-emittingelement including a dibenzo[c,g]carbazole compound in which an arylgroup is bonded to the 7-position of a dibenzo[c,g]carbazole skeletonand the aryl group has 14 to 30 carbon atoms and includes at least ananthracene skeleton. Note that when the number of carbon atoms of thearyl group is 14 to 30, the dibenzo[c,g]carbazole compound is a lowmolecular compound with a relatively low molecular weight andaccordingly has a structure suitable for vacuum evaporation (capable ofbeing vacuum-evaporated at relatively low temperature). In general, alower molecular weight tends to diminish heat resistance after filmformation. However, even with a low molecular weight, thedibenzo[c,g]carbazole compound has an advantage in that sufficient heatresistance can be ensured because of the effect of the rigiddibenzo[c,g]carbazole skeleton.

Further, the present inventors have found that a light-emitting elementusing a dibenzo[c,g]carbazole compound in which an anthracene skeletonis bonded to a dibenzo[c,g]carbazole skeleton through a phenylene groupespecially has the advantage in lifetime. The inventors have also foundthat the dibenzo[c,g]carbazole compound has an excellentcarrier-transport property and a light-emitting element using thiscompound can be driven at very low voltage.

Accordingly, another structure of the present invention is alight-emitting element including a dibenzo[c,g]carbazole compound inwhich an anthracene skeleton is bonded to the 7-position of adibenzo[c,g]carbazole skeleton through a phenylene group.

The present inventors have also found that a dibenzo[c,g]carbazolecompound in which the 7-position of a dibenzo[c,g]carbazole skeleton isbonded to the 9-position of an anthracene skeleton through a phenylenegroup especially has a wide band gap and is effective.

Accordingly, another structure of the present invention is alight-emitting element including a dibenzo[c,g]carbazole compound inwhich the 7-position of a dibenzo[c,g]carbazole skeleton is bonded tothe 9-position of an anthracene skeleton through a phenylene group.

Furthermore, the present inventors have found the favorable stabilityand reliability of the element characteristics of a light-emittingelement using a dibenzo[c,g]carbazole compound in which the number ofcarbon atoms of an anthryl phenyl group bonded to adibenzo[c,g]carbazole skeleton is 20 to 30. The present inventors havealso found the excellent driving voltage of the light-emitting element.This is probably because the dibenzo[c,g]carbazole compound can bevacuum-evaporated at relatively low temperature as described above andaccordingly is unlikely to deteriorate due to pyrolysis or the like atevaporation and because the dibenzo[c,g]carbazole compound haselectrochemical stability and a high carrier-transport property owing toits molecular structure in which an anthracene skeleton is bonded to the7-position of a dibenzo[c,g]carbazole skeleton through a phenylenegroup.

Accordingly, another structure of the present invention is alight-emitting element including a dibenzo[c,g]carbazole compound inwhich a substituted or unsubstituted anthryl phenyl group is bonded tothe 7-position of a dibenzo[c,g]carbazole skeleton and the number ofcarbon atoms of the substituted or unsubstituted anthryl phenyl group is20 to 30.

Further, the present inventors have also found the favorable stabilityand reliability of the element characteristics of a light-emittingelement using a dibenzo[c,g]carbazole compound in which the number ofcarbon atoms of (9-anthryl)phenyl group bonded to adibenzo[c,g]carbazole skeleton is 20 to 30. The present inventors havealso found the excellent driving voltage of the light-emitting element.The present inventors have also found that the compound especially has awide band gap and is effective. Thus, the dibenzo[c,g]carbazole compoundhas a wide band gap which is a feature due to the effect of the skeletonof the 9-anthryl group, in addition to the high suitability forevaporation, electrochemical stability, and carrier-transport propertydescribed above. Hence, this compound is effective in a structure of alight-emitting element in which the dibenzo[c,g]carbazole compound isused as a host material of a light-emitting layer and a light-emittingmaterial is added as a guest material to the light-emitting layer.

Accordingly, another structure of the present invention is alight-emitting element including a dibenzo[c,g]carbazole compound inwhich a substituted or unsubstituted (9-anthryl)phenyl group is bondedto the 7-position of a dibenzo[c,g]carbazole skeleton and the number ofcarbon atoms of the substituted or unsubstituted (9-anthryl)phenyl groupis 20 to 30.

Another structure of the present invention is a dibenzo[c,g]carbazolecompound represented by the following general formula (G1), with which alight-emitting element having favorable characteristics as describedabove can be easily achieved.

In the general formula (G1), Ar represents an aryl group which has 14 to30 carbon atoms and includes at least an anthracene skeleton. Further,R¹¹ to R²² each independently represent any of hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, and an aryl group having 6 to 12 carbonatoms.

In the above dibenzo[c,g]carbazole, compound represented by the generalformula (G1), when the anthracene skeleton is bonded to adibenzo[c,g]carbazole skeleton through a phenylene group, thedibenzo[c,g]carbazole compound can be synthesized with higher purity andhas an excellent carrier-transport property.

Accordingly, another structure of the present invention is adibenzo[c,g]carbazole compound represented by the following generalformula (G2).

In the general formula (G2), R¹¹ to R²² each independently represent anyof hydrogen, an alkyl group having 1 to 4 carbon atoms, and an arylgroup having 6 to 12 carbon atoms, α represents a substituted orunsubstituted phenylene group, and β represents a substituted orunsubstituted anthryl group.

In the dibenzo[c,g]carbazole compound represented by the general formula(G2), when the 7-position of a dibenzo[c,g]carbazole skeleton is bondedto the 9-position of an anthracene skeleton, the dibenzo[c,g]carbazolecompound especially has a wide band gap and is effective.

Accordingly, another structure of the present invention is adibenzo[c,g]carbazole compound represented by the following generalformula (G3).

In the general formula (G3), R⁵ represents any of hydrogen, an alkylgroup having 1 to 4 carbon atoms, and an aryl group having 6 to 10carbon atoms, R¹, R², R³, R⁴, R⁶, R⁷, R⁸, and R⁹ each independentlyrepresent hydrogen or an alkyl group having 1 to 4 carbon atoms, R¹¹ toR²² each independently represent any of hydrogen, an alkyl group having1 to 4 carbon atoms, and an aryl group having 6 to 12 carbon atoms, andα represents a substituted or unsubstituted phenylene group.

Furthermore, a light-emitting element using a dibenzo[c,g]carbazolecompound in which the number of carbon atoms of an anthryl phenyl groupbonded to a dibenzo[c,g]carbazole skeleton is 20 to 30 has elementcharacteristics with favorable stability and reliability, which is astructure preferred in terms of evaporation in the formation of alight-emitting element.

Accordingly, another structure of the present invention is adibenzo[c,g]carbazole compound represented by the following generalformula (G4).

In the general formula (G4), R¹¹ to R²² each independently represent anyof hydrogen, an alkyl group having 1 to 4 carbon atoms, and an arylgroup having 6 to 12 carbon atoms, α represents a substituted orunsubstituted phenylene group, and β represents a substituted orunsubstituted anthryl group. Note that the total number of carbon atomsof α and β is 20 to 30.

Accordingly, another structure of the present invention is adibenzo[c,g]carbazole compound represented by the following generalformula (G5).

In the general formula (G5), R⁵ represents any of hydrogen, an alkylgroup having 1 to 4 carbon atoms, and an aryl group having 6 to 10carbon atoms, R¹, R², R³, R⁴, R⁶, R⁷, R⁸, and R⁹ each independentlyrepresent hydrogen or an alkyl group having 1 to 4 carbon atoms, R¹¹ toR²² each independently represent any of hydrogen, an alkyl group having1 to 4 carbon atoms, and an aryl group having 6 to 12 carbon atoms, andα represents a substituted or unsubstituted phenylene group. Note thatthe total number of carbon atoms of R¹ to R⁹ and α is greater than orequal to 6 and less than or equal to 16.

Further, R¹, R², R³, R⁴, R⁶, R⁷, R⁸, and R⁹ are each preferably hydrogenin that synthesis becomes easy and the advantage in material cost can beobtained.

Accordingly, another structure of the present invention is adibenzo[c,g]carbazole compound represented by the following generalformula (G6).

In the general formula (G6), α represents a substituted or unsubstitutedphenylene group, R⁵ represents any of hydrogen, an alkyl group having 1to 4 carbon atoms, and an aryl group having 6 to 10 carbon atoms, andR¹¹ to R²² each independently represent any of hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, and an aryl group having 6 to 12 carbonatoms. Note that the total number of carbon atoms of R⁵ and α is greaterthan or equal to 6 and less than or equal to 16.

As in the above, R¹¹ to R²² are each preferably hydrogen, in which casea greater advantage can be drawn.

Accordingly, another structure of the present invention is adibenzo[c,g]carbazole compound represented by the following generalformula (G7).

In the general formula (G7), α represents a substituted or unsubstitutedphenylene group, and R⁵ represents any of hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, and an aryl group having 6 to 10 carbonatoms. Note that the total 0.5 number of carbon atoms of R⁵ and α isgreater than or equal to 6 and less than or equal to 16.

Another structure of the present invention is a dibenzo[c,g]carbazolecompound represented by the following structural formula (100).

Another structure of the present invention is a dibenzo[c,g]carbazolecompound represented by the following structural formula (127).

A dibenzo[c,g]carbazole compound having any of the above structures is alight-emitting element material having a wide energy gap, and can besuitably used for a transport layer, a host material, or alight-emitting substance in a blue fluorescent element or the like. Inaddition, the dibenzo[c,g]carbazole compound has a favorablecarrier-transport property, and a light-emitting element having lowdriving voltage can be provided by using the compound. Further, thedibenzo[c,g]carbazole compound is stable to oxidation and reduction, anda light-emitting element manufactured using the compound can be alight-emitting element having a long lifetime which less deteriorates.Furthermore, when the dibenzo[c,g]carbazole compound has suchcharacteristics in combination, a high-performance light-emittingelement which is excellent in emission efficiency, driving voltage, andlifetime can be manufactured.

With the use of a light-emitting element using a dibenzo[c,g]carbazolecompound, a light-emitting device, a display device, a lighting device,or an electronic device each having low power consumption can beobtained. A light-emitting device, a display device, a lighting device,or an electronic device each having high reliability can also beobtained.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B are each a conceptual diagram of a light-emittingelement;

FIG. 2 is a conceptual diagram of an organic semiconductor element;

FIGS. 3A and 3B are conceptual diagrams of an active matrixlight-emitting device;

FIGS. 4A and 4B are conceptual diagrams of a passive matrixlight-emitting device;

FIGS. 5A and 5B are conceptual diagrams of a lighting device;

FIGS. 6A to 6D illustrates electronic devices;

FIG. 7 illustrates a display device;

FIG. 8 illustrates a lighting device;

FIG. 9 illustrates lighting devices;

FIG. 10 illustrates in-vehicle display devices and lighting devices;

FIGS. 11A and 11B are NMR charts of cgDBCzPA;

FIGS. 12A and 12B each show an absorption and emission spectra ofcgDBCzPA;

FIGS. 13A and 13B are CV charts of cgDBCzPA;

FIG. 14 shows luminance versus current efficiency characteristics of alight-emitting element 1 and a comparison light-emitting element 1;

FIG. 15 shows voltage versus current characteristics of thelight-emitting element 1 and the comparison light-emitting element 1;

FIG. 16 shows luminance versus power efficiency characteristics of thelight-emitting element 1 and the comparison light-emitting element 1;

FIG. 17 shows luminance versus external quantum efficiencycharacteristics of the light-emitting element 1 and the comparisonlight-emitting element 1;

FIG. 18 shows emission spectra of the light-emitting element 1 and thecomparison light-emitting element 1;

FIG. 19 shows normalized luminance versus time characteristics of thelight-emitting element 1 and the comparison light-emitting element 1;

FIG. 20 shows luminance versus current efficiency characteristics of alight-emitting element 2 and a comparison light-emitting element 2;

FIG. 21 shows voltage versus current characteristics of thelight-emitting element 2 and the comparison light-emitting element 2;

FIG. 22 shows luminance versus power efficiency characteristics of thelight-emitting element 2 and the comparison light-emitting element 2;

FIG. 23 shows luminance versus external quantum efficiencycharacteristics of the light-emitting element 2 and the comparisonlight-emitting element 2;

FIG. 24 shows emission spectra of the light-emitting element 2 and thecomparison light-emitting element 2;

FIG. 25 shows normalized luminance versus time characteristics of alight-emitting element 2 and a comparison light-emitting element 2;

FIG. 26 shows luminance versus current efficiency characteristics of thelight-emitting element 3 and the comparison light-emitting element 3;

FIG. 27 shows voltage versus current characteristics of thelight-emitting element 3 and the comparison light-emitting element 3;

FIG. 28 shows emission spectra of the light-emitting element 3 and thecomparison light-emitting element 3;

FIG. 29 shows current density versus luminance characteristics of alight-emitting element 4 and comparison light-emitting elements 4-1 and4-2;

FIG. 30 shows luminance versus current efficiency characteristics of thelight-emitting element 4 and the comparison light-emitting elements 4-1and 4-2;

FIG. 31 shows voltage versus current characteristics of thelight-emitting element 4 and the comparison light-emitting elements 4-1and 4-2;

FIG. 32 shows luminance versus power efficiency characteristics of thelight-emitting element 4 and the comparison light-emitting elements 4-1and 4-2;

FIG. 33 shows voltage versus luminance characteristics of thelight-emitting element 4 and the comparison light-emitting elements 4-1and 4-2;

FIG. 34 shows emission spectra of the light-emitting element 4 and thecomparison light-emitting elements 4-1 and 4-2; and

FIG. 35 shows normalized luminance versus time characteristics of thelight-emitting element 4 and the comparison light-emitting elements 4-1and 4-2.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described. Itis easily understood by those skilled in the art that modes and detailsdisclosed herein can be modified in various ways without departing fromthe spirit and scope of the present invention. Therefore, the presentinvention is not construed as being limited to description of theembodiments.

Embodiment 1

A light-emitting element in this embodiment is a light-emitting elementincluding a dibenzo[c,g]carbazole compound in which an aryl groupincluding at least an anthracene skeleton is bonded to the 7-position ofa dibenzo[c,g]carbazole skeleton. Since the dibenzo[c,g]carbazolecompound has an excellent carrier-transport property, the light-emittingelement can be a light-emitting element having low driving voltage.Further, since the dibenzo[c,g]carbazole compound has high resistance torepetition of oxidation and reduction, the light-emitting element can bea light-emitting element having a long lifetime. Furthermore, since thedibenzo[c,g]carbazole compound has a wide band gap, the light-emittingelement can be a light-emitting element having high emission efficiency.As described above, a light-emitting element having a structure of thisembodiment can easily be a high-performance light-emitting elementhaving the right combination of characteristics.

Note that when the number of carbon atoms of the aryl group is 14 to 30,the dibenzo[c,g]carbazole compound is a low molecular compound with arelatively low molecular weight and accordingly has a structure suitablefor vacuum evaporation (capable of being vacuum-evaporated at relativelylow temperature). In general, a lower molecular weight tends to diminishheat resistance after film formation. However, even with a low molecularweight, the dibenzo[c,g]carbazole compound has an advantage in thatsufficient heat resistance can be ensured because of the effect of therigid dibenzo[c,g]carbazole skeleton. Note that the anthracene skeletonand the dibenzo[c,g]carbazole skeleton described above may be bondedwith an arylene group, such as a phenylene group or a naphthylene group,interposed therebetween.

Further, a light-emitting element using a dibenzo[c,g]carbazole compoundin which an anthracene skeleton is bonded to the 7-position of adibenzo[c,g]carbazole skeleton through a phenylene group especially hasthe advantage in lifetime. The dibenzo[c,g]carbazole compound has anexcellent carrier-transport property and a light-emitting element usingthis compound can be driven at very low voltage.

The above light-emitting element can be rephrased as a light-emittingelement including a dibenzo[c,g]carbazole compound in which an anthrylphenyl group is bonded to a dibenzo[c,g]carbazole skeleton. Thedibenzo[c,g]carbazole compound can be easily synthesized with highpurity, so that deterioration due to impurities can be suppressed. Notethat the number of carbon atoms of the anthryl phenyl group bonded tothe dibenzo[c,g]carbazole skeleton is preferably 20 to 30 in terms ofthe stability and reliability of element characteristics. In this case,the dibenzo[c,g]carbazole compound can be vacuum-evaporated atrelatively low temperature as described above and accordingly isunlikely to deteriorate due to pyrolysis or the like at evaporation. Inaddition, the light-emitting element is excellent in not onlyreliability but also driving voltage. This is also because ofelectrochemical stability and high carrier-transport property owing tothe molecular structure of the dibenzo[c,g]carbazole compound in whichan anthracene skeleton is bonded to the 7-position of adibenzo[c,g]carbazole skeleton through a phenylene group.

Further, a light-emitting element using a dibenzo[c,g]carbazole compoundin which the 9-position of an anthracene skeleton is bonded to the7-position of a dibenzo[c,g]carbazole skeleton is particularly suitableas a light-emitting element which exhibits light emission with largeenergy such as blue fluorescence. Note that the anthracene skeleton andthe dibenzo[c,g]carbazole skeleton described above may be bonded with anarylene group, such as a phenylene group or a naphthylene group,interposed therebetween.

For the above reason, a light-emitting element including adibenzo[c,g]carbazole compound in which the 9-position of an anthraceneskeleton is bonded to a dibenzo[c,g]carbazole skeleton through aphenylene group is preferred. In other words, a light-emitting elementincluding a dibenzo[c,g]carbazole compound in which a (9-anthryl)phenylgroup is bonded to the 7-position of a dibenzo[c,g]carbazole skeleton ispreferred. Note that the number of carbon atoms of the (9-anthryl)phenylgroup bonded to the dibenzo[c,g]carbazole skeleton is preferably 20 to30 in terms of the stability and reliability of element characteristics.Thus, the dibenzo[c,g]carbazole compound has a wide band gap which is afeature due to the effect of the skeleton of the 9-anthryl group, inaddition to the high suitability for evaporation, electrochemicalstability, and carrier-transport property described above. Hence, thiscompound is effective in a structure of a light-emitting element inwhich the dibenzo[c,g]carbazole compound is used as a host material of alight-emitting layer and a light-emitting material is added as a guestmaterial to the light-emitting layer.

Embodiment 2

In this embodiment, a dibenzo[c,g]carbazole compound used to achieve alight-emitting element described in Embodiment 1 is described.

A dibenzo[c,g]carbazole compound of this embodiment is adibenzo[c,g]carbazole compound in which an aryl group including at leastan anthracene skeleton is bonded to the 7-position of adibenzo[c,g]carbazole skeleton. The dibenzo[c,g]carbazole compound hasan excellent carrier-transport property. In addition, thedibenzo[c,g]carbazole compound has favorable resistance to repetition ofoxidation and reduction. Further, the dibenzo[c,g]carbazole compound hasa wide band gap. Accordingly, a high-performance light-emitting elementcan be easily manufactured by including a dibenzo[c,g]carbazole compoundof this embodiment.

Note that the number of carbon atoms of the aryl group bonded to thedibenzo[c,g]carbazole skeleton is preferably 14 to 30 in terms ofcharacteristics such as stability and reliability of the element to befabricated. When the number of carbon atoms of the aryl group is 14 to30, the dibenzo[c,g]carbazole compound is a low molecular compound witha relatively low molecular weight and accordingly has a structuresuitable for vacuum evaporation (capable of being vacuum-evaporated atrelatively low temperature). In general, a lower molecular weight tendsto diminish heat resistance after film formation. However, even with alow molecular weight, the dibenzo[c,g]carbazole compound has anadvantage in that sufficient heat resistance can be ensured because ofthe effect of the rigid dibenzo[c,g]carbazole skeleton. Note that inthis specification, when the number of carbon atoms is defined, thisnumber means the total number of carbon atoms including those of asubstituent of the group, compound, or the like, of which the definitionis given.

The above dibenzo[c,g]carbazole compound can be represented by thefollowing general formula (G1).

In the above general formula (G1), Ar represents a substituted orunsubstituted aryl group which has 14 to 30 carbon atoms and includes atleast an anthracene skeleton. When the anthracene skeleton has asubstituent, the substituent can be an alkyl group having 1 to 4 carbonatoms. Other than such a substituent, an aryl group having 6 to 12carbon atoms can also be selected as the substituent at the 10-positionof the anthracene skeleton. Specific examples of the alkyl group having1 to 4 carbon atoms are a methyl group, an ethyl group, a propyl group,an isopropyl group, a butyl group, an isobutyl group, a tert-butylgroup, and the like. Specific examples of the aryl group having 6 to 12carbon atoms are a phenyl group, a naphthyl group, a biphenyl group, andthe like.

Further, R¹¹ to R²² each independently represent any of hydrogen, analkyl group having 1 to 4 carbon atoms, and an aryl group having 6 to 12carbon atoms. Specific examples of the alkyl group having 1 to 4 carbonatoms are a methyl group, an ethyl group, a propyl group, an isopropylgroup, a butyl group, an isobutyl group, a tert-butyl group, and thelike. Specific examples of the aryl group having 6 to 12 carbon atomsare a phenyl group, a naphthyl group, a biphenyl group, and the like.

In the dibenzo[c,g]carbazole compound of this embodiment, it ispreferable that the anthracene skeleton be bonded to thedibenzo[c,g]carbazole skeleton through a phenylene group, in which casethe dibenzo[c,g]carbazole compound can have improved stability and canbe synthesized with higher purity. Further, since thedibenzo[c,g]carbazole compound has an excellent carrier-transportproperty, a light-emitting element using this compound can be driven atvery low voltage.

The above dibenzo[c,g]carbazole compound can be represented by thefollowing general formula (G2).

In the general formula (G2), R¹¹ to R²² each independently represent anyof hydrogen, an alkyl group having 1 to 4 carbon atoms, and an arylgroup having 6 to 12 carbon atoms. Specific examples of the alkyl grouphaving 1 to 4 carbon atoms are a methyl group, an ethyl group, a propylgroup, an isopropyl group, a butyl group, an isobutyl group, atert-butyl group, and the like. Specific examples of the aryl grouphaving 6 to 12 carbon atoms are a phenyl group, a naphthyl group, abiphenyl group, and the like.

In the general formula (G2), α represents a substituted or unsubstitutedphenylene group, and β represents a substituted or unsubstituted anthrylgroup. When a has a substituent, an alkyl group having 1 to 4 carbonatoms can be selected as the substituent. Specific examples of the alkylgroup having 1 to 4 carbon atoms are a methyl group, an ethyl group, apropyl group, an isopropyl group, a butyl group, an isobutyl group, atert-butyl group, and the like. When β has a substituent, an alkyl grouphaving 1 to 4 carbon atoms can be selected as the substituent. Otherthan such a substituent, an aryl group having 6 to 12 carbon atoms canalso be selected as the substituent at the 10-position of the anthraceneskeleton. Specific examples of the alkyl group having 1 to 4 carbonatoms are a methyl group, an ethyl group, a propyl group, an isopropylgroup, a butyl group, an isobutyl group, a tert-butyl group, and thelike. Specific examples of the aryl group having 6 to 12 carbon atomsare a phenyl group, a naphthyl group, a biphenyl group, and the like.

In the above dibenzo[c,g]carbazole compound, when the 7-position of adibenzo[c,g]carbazole skeleton is bonded to the 9-position of ananthracene skeleton, the dibenzo[c,g]carbazole compound especially has awide band gap and is effective. This is particularly effective in astructure of a light-emitting element in which the dibenzo[c,g]carbazolecompound is used as a host material of a light-emitting layer and alight-emitting material is added as a guest material to thelight-emitting layer. The above dibenzo[c,g]carbazole compound can berepresented by the following general formula (G3).

In the general formula (G3), R⁵ represents any of hydrogen, an alkylgroup having 1 to 4 carbon atoms, and an aryl group having 6 to 10carbon atoms. Specific examples of the alkyl group having 1 to 4 carbonatoms are a methyl group, an ethyl group, a propyl group, an isopropylgroup, a butyl group, an isobutyl group, a tert-butyl group, and thelike. Specific examples of the aryl group having 6 to 10 carbon atomsare a phenyl group, a naphthyl group, and the like. Further, R¹, R², R³,R⁴, R⁶, R⁷, R⁸, and R⁹ each independently represent hydrogen or an alkylgroup having 1 to 4 carbon atoms. Specific examples of the alkyl grouphaving 1 to 4 carbon atoms are a methyl group, an ethyl group, a propylgroup, an isopropyl group, a butyl group, an isobutyl group, atert-butyl group, and the like. Further, R¹¹ to R²² each independentlyrepresent any of hydrogen, an alkyl group having 1 to 4 carbon atoms,and an aryl group having 6 to 12 carbon atoms. Specific examples of thealkyl group having 1 to 4 carbon atoms are a methyl group, an ethylgroup, a propyl group, an isopropyl group, a butyl group, an isobutylgroup, a tert-butyl group, and the like. Specific examples of the arylgroup having 6 to 12 carbon atoms are a phenyl group, a naphthyl group,a biphenyl group, and the like. In addition, α represents a substitutedor unsubstituted phenylene group. When α has a substituent, an alkylgroup having 1 to 4 carbon atoms can be selected as the substituent.Specific examples of the alkyl group having 1 to 4 carbon atoms are amethyl group, an ethyl group, a propyl group, an isopropyl group, abutyl group, an isobutyl group, a tert-butyl group, and the like.

Note that the dibenzo[c,g]carbazole compound represented by the generalformula (G2) can be rephrased as a dibenzo[c,g]carbazole compound inwhich a phenyl anthryl group is bonded to a dibenzo[c,g]carbazoleskeleton, and the dibenzo[c,g]carbazole compound represented by thegeneral formula (G3) can be rephrased as a dibenzo[c,g]carbazolecompound in which a (9-phenyl)anthryl group is bonded to adibenzo[c,g]carbazole skeleton. Hence, the number of carbon atoms of thephenyl anthryl group or (9-phenyl)anthryl group bonded to thedibenzo[c,g]carbazole skeleton is preferably 20 to 30 in terms ofcharacteristics such as stability and reliability of the element to befabricated. This is probably because the dibenzo[c,g]carbazole compoundcan be vacuum-evaporated at relatively low temperature as describedabove and accordingly is unlikely to deteriorate due to pyrolysis or thelike at evaporation. Note that a dibenzo[c,g]carbazole compound having a(9-phenyl)anthryl group especially has a wide band gap and therefore canbe suitably used as a host material of a light-emitting layer in alight-emitting element.

The dibenzo[c,g]carbazole compound has electrochemical stability and ahigh carrier-transport property owing to its molecular structure inwhich an anthracene skeleton is bonded to the 7-position of adibenzo[c,g]carbazole skeleton through a phenylene group.

The above dibenzo[c,g]carbazole compound can be represented by thefollowing general formula (G4) or (G5).

In the general formula (G4), R¹¹ to R²² each independently represent anyof hydrogen, an alkyl group having 1 to 4 carbon atoms, and an arylgroup having 6 to 12 carbon atoms. Specific examples of the alkyl grouphaving 1 to 4 carbon atoms are a methyl group, an ethyl group, a propylgroup, an isopropyl group, a butyl group, an isobutyl group, atert-butyl group, and the like. Specific examples of the aryl grouphaving 6 to 12 carbon atoms are a phenyl group, a naphthyl group, abiphenyl group, and the like. In addition, α represents a substituted orunsubstituted phenylene group. When α has a substituent, an alkyl grouphaving 1 to 4 carbon atoms can be selected as the substituent. Specificexamples of the alkyl group having 1 to 4 carbon atoms are a methylgroup, an ethyl group, a propyl group, an isopropyl group, a butylgroup, an isobutyl group, a tert-butyl group, and the like. Further, βrepresents a substituted or unsubstituted anthryl group. When β has asubstituent, an alkyl group having 1 to 4 carbon atoms can be selectedas the substituent. Other than such a substituent, an aryl group having6 to 12 carbon atoms can also be selected as the substituent at the10-position of the anthracene skeleton. Specific examples of the alkylgroup having 1 to 4 carbon atoms are a methyl group, an ethyl group, apropyl group, an isopropyl group, a butyl group, an isobutyl group, atert-butyl group, and the like. Specific examples of the aryl grouphaving 6 to 12 carbon atoms are a phenyl group, a naphthyl group, abiphenyl group, and the like. Note that the total number of carbon atomsof α and β is 20 to 30.

In the general formula (G5), R⁵ represents any of hydrogen, an alkylgroup having 1 to 4 carbon atoms, and an aryl group having 6 to 10carbon atoms. Specific examples of the alkyl group having 1 to 4 carbonatoms are a methyl group, an ethyl group, a propyl group, an isopropylgroup, a butyl group, an isobutyl group, a tert-butyl group, and thelike. Specific examples of the aryl group having 6 to 10 carbon atomsare a phenyl group; a naphthyl group, and the like. Further, R¹, R², R³,R⁴, R⁶, R⁷, R⁸, and R⁹ each independently represent hydrogen or an alkylgroup having 1 to 4 carbon atoms. Specific examples of the alkyl grouphaving 1 to 4 carbon atoms are a methyl group, an ethyl group, a propylgroup, an isopropyl group, a butyl group, an isobutyl group, atert-butyl group, and the like. Further, R¹¹ to R²² each independentlyrepresent any of hydrogen, an alkyl group having 1 to 4 carbon atoms,and an aryl group having 6 to 12 carbon atoms. Specific examples of thealkyl group having 1 to 4 carbon atoms are a methyl group, an ethylgroup, a propyl group, an isopropyl group, a butyl group, an isobutylgroup, a tert-butyl group, and the like. Specific examples of the arylgroup having 6 to 12 carbon atoms are a phenyl group, a naphthyl group,a biphenyl group, and the like. In addition, α represents a substitutedor unsubstituted phenylene group. When α has a substituent, an alkylgroup having 1 to 4 carbon atoms can be selected as the substituent.Specific examples of the alkyl group having 1 to 4 carbon atoms are amethyl group, an ethyl group, a propyl group, an isopropyl group, abutyl group, an isobutyl group, a tert-butyl group, and the like. Notethat the total number of carbon atoms of R¹ to R⁹ and α is greater thanor equal to 6 and less than or equal to 16.

Further, R¹, R², R³, R⁴, R⁶, R⁷, R⁸, and R⁹ are each preferably hydrogenin that synthesis becomes easy and the advantage in material cost can beobtained.

Accordingly, another structure of the present invention is adibenzo[c,g]carbazole compound represented by the following generalformula (G6).

In the general formula (G6), α represents a substituted or unsubstitutedphenylene group. When α has a substituent, an alkyl group having 1 to 4carbon atoms can be selected as the substituent. Specific examples ofthe alkyl group having 1 to 4 carbon atoms are a methyl group, an ethylgroup, a propyl group, an isopropyl group, a butyl group, an isobutylgroup, a tert-butyl group, and the like. Further, R⁵ represents any ofhydrogen, an alkyl group having 1 to 4 carbon atoms, and an aryl grouphaving 6 to 10 carbon atoms. Specific examples of the alkyl group having1 to 4 carbon atoms are a methyl group, an ethyl group, a propyl group,an isopropyl group, a butyl group, an isobutyl group, a tert-butylgroup, and the like. Further, R¹¹ to R²² each independently representany of hydrogen, an alkyl group having 1 to 4 carbon atoms, and an arylgroup having 6 to 12 carbon atoms. Specific examples of the alkyl grouphaving 1 to 4 carbon atoms are a methyl group, an ethyl group, a propylgroup, an isopropyl group, a butyl group, an isobutyl group, atert-butyl group, and the like. Note that the total number of carbonatoms of R⁵ and α is greater than or equal to 6 and less than or equalto 16.

As in the above, R¹¹ to R²² are each preferably hydrogen, in which casea greater advantage can be drawn.

Accordingly, another structure of the present invention is adibenzo[c,g]carbazole compound represented by the following generalformula (G7).

In the general formula (G7), α represents a substituted or unsubstitutedphenylene group. When α has a substituent, an alkyl group having 1 to 4carbon atoms can be selected as the substituent. Specific examples ofthe alkyl group having 1 to 4 carbon atoms are a methyl group, an ethylgroup, a propyl group, an isopropyl group, a butyl group, an isobutylgroup, a tert-butyl group, and the like. Further, R⁵ represents any ofhydrogen, an alkyl group having 1 to 4 carbon atoms, and an aryl grouphaving 6 to 10 carbon atoms. Specific examples of the alkyl group having1 to 4 carbon atoms are a methyl group, an ethyl group, a propyl group,an isopropyl group, a butyl group, an isobutyl group, a tert-butylgroup, and the like. Note that the total number of carbon atoms of R⁵and α is greater than or equal to 6 and less than or equal to 16.

As the aryl group represented by Ar in the above general formula (G1),for example, groups represented by structural formulae (Ar-1) to (Ar-51)below can be used. Note that a group that can be used as Ar is notlimited to these.

As the aryl group represented by R¹¹ to R²² in the above generalformulae (G1) to (G6), for example, groups represented by structuralformulae (Rc-1) to (Rc-17) below can be used. Note that a group that canbe used as R¹¹ to R²² is not limited to these.

As the aryl group represented by α in the above general formulae (G2) to(G7), for example, groups represented by structural formulae (α-1) to(α-11) below can be used. Note that a group that can be used as α is notlimited to these.

As the aryl group represented by β in the above general formulae (G2)and (G4), for example, groups represented by structural formulae (β-1)to (β-37) below can be used. Note that a group that can be used as β isnot limited to these.

As the aryl group represented by R¹, R², R³, R⁴, R⁶, R⁷, R⁵, and R⁹ inthe above general formulae (G3) and (G5), for example, groupsrepresented by structural formulae (Ra-1) to (Ra-9) below can be used.Note that a group that can be used as R¹, R², R³, R⁴, R⁶, R⁷, R⁸, and R⁹is not limited to these.

As the aryl group represented by R⁵ in the above general formulae (G3)and (G5) to (G7), for example, groups represented by structural formulae(R⁵-1) to (R⁵-17) below can be used. Note that a group that can be usedas R⁵ is not limited to these.

Specific examples of structures of the dibenzo[c,g]carbazole compoundsrepresented by the above general formulae (G1) to (G7) are substancesrepresented by structural formulae (100) to (136) below, and the like.Note that the dibenzo[c,g]carbazole compounds represented by the abovegeneral formulae (G1) to (G7) are not limited to the following examples.

Since a dibenzo[c,g]carbazole compound described above has an excellentcarrier-transport property, it is suitable as a carrier-transportmaterial or a host material. Accordingly, a light-emitting elementhaving low driving voltage can also be provided. Further, adibenzo[c,g]carbazole compound in this embodiment has excellentstability to oxidation and reduction. Accordingly, a light-emittingelement using a dibenzo[c,g]carbazole compound can be a light-emittingelement having a long lifetime. Furthermore, a dibenzo[c,g]carbazolecompound in this embodiment has a sufficiently wide band gap, andaccordingly, even when it is used as a host material of a bluefluorescent material, a light-emitting element with high emissionefficiency can be obtained.

Embodiment 3

Next, in this embodiment, a method of synthesizing thedibenzo[c,g]carbazole compound represented by the general formula (G1)is described. A variety of reactions can be applied to the method ofsynthesizing the dibenzo[c,g]carbazole compound. For example, synthesisreactions described below enable the synthesis of thedibenzo[c,g]carbazole compound represented by the general formula (G1).Note that the method of synthesizing a dibenzo[c,g]carbazole compound ofone embodiment of the present invention is not limited to the followingsynthesis methods.

Synthesis Method of Dibenzo[c,g]carbazole Compound Represented byGeneral Formula (G1)

The dibenzo[c,g]carbazole compound (G1) of the present invention can besynthesized in accordance with a synthesis scheme (A-1) illustratedbelow. Specifically, an anthracene compound (compound 1) and adibenzo[c,g]carbazole compound (compound 2) undergo coupling, wherebythe dibenzo[c,g]carbazole compound (G1) of the present invention can beobtained.

In the synthesis scheme (A-1), Ar represents a substituted orunsubstituted aryl group which has 14 to 30 carbon atoms and includes atleast an anthracene skeleton. Further, R¹¹ to R²² each independentlyrepresent any of hydrogen, an alkyl group having 1 to 4 carbon atoms,and an aryl group having 6 to 12 carbon atoms.

In the case where a Hartwig-Buchwald reaction using a palladium catalystis performed in the synthesis scheme (A-1), X represents a halogen or atriflate group. As the halogen, iodine, bromine, or chlorine ispreferable. A palladium catalyst using a palladium compound such asbis(dibenzylideneacetone)palladium(0) or palladium(II)acetate and aligand that coordinates to the palladium compound, such astri(tert-butyl)phosphine, tri(n-hexyl)phosphine, ortricyclohexylphosphine, is used for the reaction. As a base, an organicbase such as sodium tert-butoxide, an inorganic base such as potassiumcarbonate or sodium carbonate, and the like can be used for thereaction. In the case where a solvent is used, toluene, xylene, benzene,tetrahydrofuran, or the like can be used. Note that reagents which canbe used for the reaction are not limited to the above.

In the case where an Ullmann reaction using copper or a copper compoundis performed in the synthesis scheme (A-1), X represents a halogen. Asthe halogen, iodine, bromine, or chlorine is preferable. As a catalyst,copper or a copper compound is used for the reaction. As the base whichis used, an inorganic base such as potassium carbonate can be given.Examples of solvents which can be used for the reaction are1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU), toluene,xylene, benzene, and the like. In an Ullmann reaction, DMPU or xylene,which has a high boiling point, is preferably used, in which case theobject of the synthesis can be obtained in a shorter time and a higheryield at a reaction temperature of 100° C. or more. A reactiontemperature of 150° C. or more is further preferred and accordingly DMPUis more preferably used. Note that reagents which can be used for thereaction are not limited to the above.

In the above manner, a dibenzo[c,g]carbazole compound described inEmbodiment 2 can be synthesized.

Embodiment 4

In this embodiment is described an example of the mode where adibenzo[c,g]carbazole compound described in Embodiment 2 is used for anactive layer of a vertical transistor (static induction transistor:SIT), which is a kind of an organic semiconductor element.

As illustrated in FIG. 2, the element has a structure in which athin-film active layer 1202 containing a dibenzo[c,g]carbazole compounddescribed in Embodiment 2 is provided between a source electrode 1201and a drain electrode 1203, and a gate electrode 1204 is embedded in theactive layer 1202. The gate electrode 1204 is electrically connected toa means for applying a gate voltage, and the source electrode 1201 andthe drain electrode 1203 are electrically connected to a means forcontrolling a voltage between a source electrode and a drain electrode.

In such an element structure, when a voltage is applied between thesource electrode and the drain electrode without applying a voltage tothe gate electrode, current flows (on state). Then, by application of avoltage to the gate electrode in that state, a depletion layer is formedin the periphery of the gate electrode 1204, and the current ceasesflowing (off state). With such a mechanism, the element operates as atransistor.

Like a light-emitting element, a vertical transistor should contain amaterial that can achieve both a high carrier-transport property andhigh film quality for an active layer; a dibenzo[c,g]carbazole compounddescribed in Embodiment 2 meets such a requirement and therefore can besuitably used.

Embodiment 5

In this embodiment, a detailed example of the structure of alight-emitting element described in Embodiment 1 is described below withreference to FIG. 1A.

A light-emitting element in this embodiment includes a plurality oflayers between a pair of electrodes. In this embodiment, thelight-emitting element includes a first electrode 101, a secondelectrode 102, and an EL layer 103, which is provided between the firstelectrode 101 and the second electrode 102. Note that in thisembodiment, the first electrode 101 functions as an anode and the secondelectrode 102 functions as a cathode. In other words, when a voltage isapplied between the first electrode 101 and the second electrode 102 sothat the potential of the first electrode 101 is higher than that of thesecond electrode 102, light emission can be obtained. A light-emittingelement in this embodiment is a light-emitting element in which adibenzo[c,g]carbazole compound is used for any of layers in the EL layer103.

For the first electrode 101, any of metals, alloys, electricallyconductive compounds, and mixtures thereof which have a high workfunction (specifically, a work function of 4.0 eV or more) or the likeis preferably used. Specifically, for example, indium oxide-tin oxide(ITO: indium tin oxide), indium oxide-tin oxide containing silicon orsilicon oxide, indium oxide-zinc oxide (indium zinc oxide), indium oxidecontaining tungsten oxide and zinc oxide (IWZO), and the like can begiven. Films of these electrically conductive metal oxides are usuallyformed by sputtering but may be formed by application of a sol-gelmethod or the like. For example, indium oxide-zinc oxide can be formedby a sputtering method using a target in which zinc oxide is added toindium oxide at 1 wt % to 20 wt %. Moreover, indium oxide containingtungsten oxide and zinc oxide (IWZO) can be formed by a sputteringmethod using a target in which tungsten oxide is added to indium oxideat 0.5 wt % to 5 wt % and zinc oxide is added to indium oxide at 0.1 wt% to 1 wt %. Besides, gold (Au), platinum (Pt), nickel (Ni), tungsten(W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper(Cu), palladium (Pd), graphene, nitrides of metal materials (e.g.,titanium nitride), and the like can be given.

There is no particular limitation on a stacked structure of the EL layer103. The EL layer 103 can be formed by combining a layer that contains asubstance having a high electron-transport property, a layer thatcontains a substance having a high hole-transport property, a layer thatcontains a substance having a high electron-injection property, a layerthat contains a substance having a high hole-injection property, a layerthat contains a bipolar substance (a substance having a highelectron-transport and hole-transport property), and the like asappropriate. For example, the EL layer 103 can be formed by combining ahole-injection layer, a hole-transport layer, a light-emitting layer, anelectron-transport layer, an electron-injection layer, and the like asappropriate. In this embodiment, the EL layer 103 has a structure inwhich a hole-injection layer 111, a hole-transport layer 112, alight-emitting layer 113, an electron-transport layer 114, and anelectron-injection layer 115 are stacked in this order over the firstelectrode 101. Materials included in the layers are specifically givenbelow.

The hole-injection layer 111 is a layer containing a substance having ahigh hole-injection property. Molybdenum oxide, vanadium oxide,ruthenium oxide, tungsten oxide, manganese oxide, or the like can beused. Alternatively, the hole-injection layer 111 can be formed with aphthalocyanine-based compound such as phthalocyanine (abbreviation:H₂Pc) or copper phthalocyanine (abbreviation: CuPc), an aromatic aminecompound such as4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB) orN,N′-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine(abbreviation: DNTPD), a high molecular compound such aspoly(ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS), orthe like.

Alternatively, a composite material in which a substance having a highhole-transport property contains a substance having an acceptor propertycan be used for the hole-injection layer 111. Note that the use of sucha substance having a high hole-transport property which contains asubstance having an acceptor property enables selection of a materialused to form an electrode regardless of its work function. In otherwords, besides a material having a high work function, a material havinga low work function can also be used for the first electrode 101. As thesubstance having an acceptor property,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, and the like can be given. In addition, transitionmetal oxides can be given. Oxides of the metals that belong to Group 4to Group 8 of the periodic table can be given. Specifically, vanadiumoxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide,tungsten oxide, manganese oxide, and rhenium oxide are preferable inthat their electron-accepting property is high. Among these, molybdenumoxide is especially preferable in that it is stable in the air, has alow hygroscopic property, and is easily treated.

As the substance having a high hole-transport property used for thecomposite material, any of a variety of compounds such as aromatic aminecompounds, carbazole derivatives, aromatic hydrocarbons, and highmolecular compounds (e.g., oligomers, dendrimers, or polymers) can beused. Note that the organic compound used for the composite material ispreferably an organic compound having a high hole-transport property.Specifically, a substance having a hole mobility of 10⁻⁶ cm²/Vs or moreis preferably used. Further, other than these substances, any substancethat has a property of transporting more holes than electrons may beused. Organic compounds that can be used as the substance having a highhole-transport property in the composite material are specifically givenbelow.

Examples of the aromatic amine compounds areN,N′-di(p-tolyl)-N,N′-diphenyl-p-phenylenediamine (abbreviation:DTDPPA), 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl(abbreviation: DPAB),N,N′-bis{4-[bis(3-methylphenyl)amino]phenyl}-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine(abbreviation: DNTPD),1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B), and the like.

Specific examples of the carbazole derivatives that can be used for thecomposite material are3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2),3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1), and the like.

Other examples of the carbazole derivatives that can be used for thecomposite material are 4,4′-di(N-carbazolyl)biphenyl (abbreviation:CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB),9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA),1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene, and thelike.

Examples of the aromatic hydrocarbons that can be used for the compositematerial are 2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation:t-BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA),2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA),9,10-di(2-naphthyl)anthracene (abbreviation: DNA),9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene(abbreviation: t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene(abbreviation: DMNA),2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene,9,10-bis[2-(1-naphthyl)phenyl]anthracene,2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene,2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl,10,10′-diphenyl-9,9′-bianthryl,10,10′-bis(2-phenylphenyl)-9,9′-bianthryl,10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene,tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene, andthe like. Besides, pentacene, coronene, or the like can also be used.Thus, an aromatic hydrocarbon having 14 to 42 carbon atoms or more andhaving a hole mobility of 1×10⁻⁶ cm²/Vs is more preferably used.

Note that the aromatic hydrocarbons that can be used for the compositematerial may have a vinyl skeleton. Examples of the aromatic hydrocarbonhaving a vinyl group are 4,4′-bis(2,2-diphenylvinyl)biphenyl(abbreviation: DPVBi), 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene(abbreviation: DPVPA), and the like.

A high molecular compound such as poly(N-vinylcarbazole) (abbreviation:PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), orpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:poly-TPD) can also be used.

The hole-transport layer 112 is a layer that contains a substance havinga high hole-transport property. Examples of the substance having a highhole-transport property are aromatic amine compounds such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine(abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA), and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB), and the like. The substances mentioned here aremainly ones that have a hole mobility of 10⁻⁶ cm²/Vs or more. An organiccompound given as an example of the substance having a highhole-transport property in the composite material described above canalso be used for the hole-transport layer 112. A high molecular compoundsuch as poly(N-vinylcarbazole) (abbreviation: PVK) orpoly(4-vinyltriphenylamine) (abbreviation: PVTPA) can also be used.However, other than these substances, a substance that has a property oftransporting more holes than electrons may be used. Further, the layerthat includes a substance having a high hole-transport property is notlimited to a single layer, and may be a stack of two or more layersincluding any of the above substances.

A dibenzo[c,g]carbazole compound described in Embodiment 2 may be usedas a material included in the hole-transport layer 112.

The light-emitting layer 113 is a layer containing a light-emittingsubstance. The light-emitting layer 113 may be formed with a filmcontaining only a light-emitting substance or a film in which anemission center substance is dispersed into a host material.

There is no particular limitation on a material that can be used as thelight-emitting substance or the emission center substance in thelight-emitting layer 113, and light emitted from the material may beeither fluorescence or phosphorescence. Examples of the abovelight-emitting substance or emission center substance are the followingsubstances: fluorescent substances such asN,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenyl-pyrene-1,6-diamine(abbreviation: 1,6-FLPAPrn),N,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine(abbreviation: 2YGAPPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA), perylene, 2,5,8,11-tetra-tert-butylperylene(abbreviation: TBP),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA),N,N″-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N′,N′-triphenyl-1,4-phenylenediamine](abbreviation: DPABPA),N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: 2PCAPPA),N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPPA),N,N,N′,N′,N″,N″,N′″N′″-octaphenyldibenzo[g,p]chysene-2,7,10,15-tetraamine(abbreviation: DBC1), coumarin 30,N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),9,10-bis(1,1′-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(abbreviation: 2YGABPhA), N,N,9-triphenylanthracen-9-amine(abbreviation: DPhAPhA), coumarin 545T, N,N′-diphenylquinacridone(abbreviation: DPQd), rubrene,5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT),2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)propanedinitrile(abbreviation: DCM1),2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCM2),N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation:p-mPhTD),7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD),2-{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTI),2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTB),2-(2,6-bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile(abbreviation: BisDCM), and2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: BisDCJTM); and phosphorescent substances such asbis[2-(3′,5′-bistrifluoromethylphenyl)pyridinato-N,C^(2′)]iridium(III)picolinate(abbreviation: Ir(CF₃ppy)₂(pic)),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate(abbreviation: FIracac),tris(2-phenylpyridinato)iridium(III)(abbreviation: Ir(ppy)₃),bis(2-phenylpyridinato)iridium(III)acetylacetonate (abbreviation:Ir(ppy)₂(acac)), tris(acetylacetonato)(monophenanthroline)terbium(III)(abbreviation: Tb(acac)₃(Phen)),bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation:Ir(bzq)₂(acac)),bis(2,4-diphenyl-1,3-oxazolato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(dpo)₂(acac)),bis[2-(4′-perfluorophenylphenyl)pyridinato]iridium(III)acetylacetonate(abbreviation: Ir(p-PF-ph)₂(acac)),bis(2-phenylbenzothiazolato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(bt)₂(acac)),bis[2-(2′-benzo[4,5-α]thienyl)pyridinato-N,C^(3′)]iridium(III)(acetylacetonate)(abbreviation: Ir(btp)₂(acac)),bis(1-phenylisoquinolinato-N,C^(2′))iridium(III)acetylacetonate(abbreviation: Ir(piq)₂(acac)),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: Ir(Fdpq)₂(acac)),(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)),2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum(II)(abbreviation: PtOEP),tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III)(abbreviation: Eu(DBM)₃ (Phen)), andtris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III)(abbreviation: Eu(TTA)₃(Phen)). Note that a dibenzo[c,g]carbazolecompound described in Embodiment 2 can also be used as a light-emittingmaterial or an emission center material. The dibenzo[c,g]carbazolecompound is an emission center substance which emits light having aspectrum in a range from purple to blue.

Although there is no particular limitation on a material that can beused as the host material described above, any of the followingsubstances can be used for the host material, for example: metalcomplexes such as tris(8-quinolinolato)aluminum(III) (abbreviation:Alq), tris(4-methyl-8-quinolinolato)aluminum(III) (abbreviation: Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III)(abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq),bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), andbis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ);heterocyclic compounds such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI), bathophenanthroline (abbreviation: BPhen),bathocuproine (abbreviation: BCP), and9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation:CO11); and aromatic amine compounds such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB). In addition, condensed polycyclic aromaticcompounds such as anthracene derivatives, phenanthrene derivatives,pyrene derivatives, chrysene derivatives, and dibenzo[g,p]chysenederivatives can be given, and specific examples are9,10-diphenylanthracene (abbreviation: DPAnth),N,N-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: CzA1PA), 4-(10-phenyl-9-anthryl)triphenylamine(abbreviation: DPhPA),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA),N,9-diphenyl-N-{4-[4-(10-phenyl-9-anthryl)phenyl]phenyl}-9H-carbazol-3-amine(abbreviation: PCAPBA),N,9-diphenyl-N-(9,10-diphenyl-2-anthryl)-9H-carbazol-3-amine(abbreviation: 2PCAPA), 6,12-dimethoxy-5,11-diphenylchrysene,N,N,N′,N′,N″,N″,N′″,N′″-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetramine(abbreviation: DBC1), 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: CzPA),3,6-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: DPCzPA), 9,10-bis(3,5-diphenylphenyl)anthracene(abbreviation: DPPA), 9,10-di(2-naphthyl)anthracene (abbreviation: DNA),2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA),9,9′-bianthryl (abbreviation: BANT),9,9′-(stilbene-3,3′-diyl)diphenanthrene (abbreviation: DPNS),9,9′-(stilbene-4,4′-diyl)diphenanthrene (abbreviation: DPNS2),3,3′,3″-(benzene-1,3,5-triyl)tripyrene (abbreviation: TPB3), and thelike. Further, a dibenzo[c,g]carbazole compound described in Embodiment2 can also be suitably used as a host material. One or more substanceshaving a wider energy gap than the emission center substance describedabove is preferably selected from these substances and known substances.Moreover, in the case where the emission center substance is a substancewhich emits phosphorescence, a substance having higher tripletexcitation energy (energy difference between a ground state and atriplet excitation state) than the emission center substance can beselected as the host material.

Note that a dibenzo[c,g]carbazole compound described in Embodiment 2 canbe suitably used in a light-emitting element whose emission centersubstance is a substance which emits blue fluorescence. This is becausethe wide band gap of the dibenzo[c,g]carbazole compound enables asubstance which emits blue fluorescence to be effectively excited, sothat a light-emitting element which provides blue fluorescence with highemission efficiency can be easily provided. Further, since adibenzo[c,g]carbazole compound described in Embodiment 2 has anexcellent carrier-transport property, a light-emitting element havinglow driving voltage can be provided.

Note that the light-emitting layer 113 can also be a stack of two ormore layers. For example, in the case where the light-emitting layer 113is formed by stacking a first light-emitting layer and a secondlight-emitting layer in that order over the hole-transport layer, asubstance having a hole-transport property is used for the host materialof the first light-emitting layer and a substance having anelectron-transport property is used for the host material of the secondlight-emitting layer.

In the case where the light-emitting layer having the above-describedstructure includes a plurality of materials, co-evaporation by a vacuumevaporation method can be used, or alternatively an inkjet method, aspin coating method, a dip coating method, or the like with a solutionof the materials can be used.

The electron-transport layer 114 is a layer containing a substancehaving a high electron-transport property. For example, a layercontaining a metal complex having a quinoline skeleton or abenzoquinoline skeleton, such as tris(8-quinolinolato)aluminum(abbreviation: Alq), tris(4-methyl-8-quinolinolato)aluminum(abbreviation: Almq₃), bis(10-hydroxybenzo[h]quinolinato)beryllium(abbreviation: BeBq₂), orbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq). Alternatively, a metal complex having an oxazole-based orthiazole-based ligand, such as bis[2-(2-hydroxyphenyl)benzoxazolato]zinc(abbreviation: Zn(BOX)₂) or bis[2-(2-hydroxyphenyl)benzothiazolato]zinc(abbreviation: Zn(BTZ)₂), or the like can be used. Besides the metalcomplexes, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole(abbreviation: PBD),1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ), bathophenanthroline (abbreviation: BPhen),bathocuproine (abbreviation: BCP), or the like can also be used. Adibenzo[c,g]carbazole compound described in Embodiment 2 can also besuitably used. The substances mentioned here mainly have an electronmobility of 10⁻⁶ cm²/Vs or more. Note that other than these substances,a substance that has a property of transporting more electrons thanholes may be used for the electron-transport layer.

Furthermore, the electron-transport layer 114 is not limited to a singlelayer and may be a stack of two or more layers containing any of theabove substances.

Between the electron-transport layer and the light-emitting layer, alayer that controls transport of electron carriers may be provided. Thisis a layer formed by addition of a small amount of a substance having ahigh electron-trapping property to a material having a highelectron-transport property as described above, and the layer is capableof adjusting carrier balance by suppressing transport of electroncarriers. Such a structure is very effective in preventing a problem(such as a reduction in element lifetime) caused when electrons passthrough the light-emitting layer.

Since a dibenzo[c,g]carbazole compound described in Embodiment 2 has anexcellent carrier-transport property, by using the compound as amaterial of the electron-transport layer 114, a light-emitting elementhaving low driving voltage can be easily provided. Further, since thedibenzo[c,g]carbazole compound has a wide band gap, even when thecompound is used as a material of the electron-transport layer 114adjacent to the light-emitting layer 113, there is less possibility ofdeactivation of the excitation energy of the emission center substanceand a light-emitting element with high emission efficiency can be easilyprovided.

In addition, an electron-injection layer 115 may be provided in contactwith the second electrode 102 between the electron-transport layer 114and the second electrode 102. For the electron-injection layer 115, analkali metal, an alkaline earth metal, or a compound thereof such aslithium fluoride (LiF), cesium fluoride (CsF), or calcium fluoride(CaF₂) can be used. For example, a layer that is formed with a substancehaving an electron-transport property and contains an alkali metal, analkaline earth metal, magnesium (Mg), or a compound thereof can be used.For example, an Alq layer containing magnesium (Mg) can be used. Notethat electron injection from the second electrode 102 is efficientlyperformed with the use of a layer that is formed with a substance havingan electron-transport property and contains an alkali metal or analkaline earth metal as the electron-injection layer 115, which ispreferable.

For the second electrode 102, any of metals, alloys, electricallyconductive compounds, and mixtures thereof which have a low workfunction (specifically, a work function of 3.8 eV or less) or the likecan be used. Specific examples of such a cathode material includeelements that belong to Groups 1 and 2 in the periodic table, i.e.,alkali metals such as lithium (Li) and cesium (Cs), and alkaline earthmetals such as magnesium (Mg), calcium (Ca), and strontium (Sr), alloysthereof (e.g., MgAg or AlLi), rare earth metals such as europium (Eu)and ytterbium (Yb), alloys thereof, and the like. However, when theelectron-injection layer is provided between the second electrode 102and the electron-transport layer, for the second electrode 102, any of avariety of conductive materials such as Al, Ag, ITO, or indium oxide-tinoxide containing silicon or silicon oxide can be used regardless of thework function. Films of these electrically conductive materials can beformed by a sputtering method, an inkjet method, a spin coating method,or the like.

Further, any of a variety of methods can be used to form the EL layer103 regardless whether it is a dry process or a wet process. Forexample, a vacuum evaporation method, an inkjet method, a spin coatingmethod or the like may be used. Different formation methods may be usedfor the electrodes or the layers.

In addition, the electrode may be formed by a wet method using a sol-gelmethod, or by a wet method using paste of a metal material.Alternatively, the electrode may be formed by a dry method such as asputtering method or a vacuum evaporation method.

In the light-emitting element having the above-described structure,current flows due to a potential difference between the first electrode101 and the second electrode 102, and holes and electrons recombine inthe light-emitting layer 113 which contains a substance having a highlight-emitting property, so that light is emitted. That is, alight-emitting region is formed in the light-emitting layer 113.

Light emission is extracted out through one or both of the firstelectrode 101 and the second electrode 102. Therefore, one or both ofthe first electrode 101 and the second electrode 102 arelight-transmitting electrodes. In the case where only the firstelectrode 101 is a light-transmitting electrode, light emission isextracted through the first electrode 101. In the case where only thesecond electrode 102 is a light-transmitting electrode, light emissionis extracted through the second electrode 102. In the case where boththe first electrode 101 and the second electrode 102 arelight-transmitting electrodes, light emission is extracted through thefirst electrode 101 and the second electrode 102.

The structure of the layers provided between the first electrode 101 andthe second electrode 102 is not limited to the above-describedstructure. Preferably, a light-emitting region where holes and electronsrecombine is positioned away from the first electrode 101 and the secondelectrode 102 so that quenching due to the proximity of thelight-emitting region and a metal used for electrodes andcarrier-injection layers can be prevented.

Further, in order that transfer of energy from an exciton generated inthe light-emitting layer can be suppressed, preferably, thehole-transport layer and the electron-transport layer which are indirect contact with the light-emitting layer, particularly acarrier-transport layer in contact with a side closer to thelight-emitting region in the light-emitting layer 113 is formed with asubstance having a larger energy gap than the light-emitting substanceof the light-emitting layer or the emission center substance included inthe light-emitting layer.

In a light-emitting element in this embodiment, when adibenzo[c,g]carbazole compound described in Embodiment 2 is used for thehole-transport layer or the electron-transport layer, efficient lightemission is possible even with the light-emitting substance or theemission center substance that has a large energy gap and emits bluefluorescence or green phosphorescence with large triplet excitationenergy (an energy difference between a ground state and a tripletexcited state); thus, a light-emitting element having high emissionefficiency can be obtained. Accordingly, a light-emitting element havinghigher emission efficiency and lower power consumption can be provided.In addition, a light-emitting element capable of light emission withhigh color purity can be provided. Further, a dibenzo[c,g]carbazolecompound described in Embodiment 2 has an excellent carrier-transportproperty; thus, a light-emitting element having low driving voltage canbe provided.

Since a dibenzo[c,g]carbazole compound described in Embodiment 2 isstable to repetition of oxidation and reduction, a light-emittingelement having a long lifetime can be easily provided by using thedibenzo[c,g]carbazole compound.

A light-emitting element in this embodiment is preferably fabricatedover a substrate of glass, plastic, or the like. As the way of stackinglayers over the substrate, layers may be sequentially stacked on thefirst electrode 101 side or sequentially stacked on the second electrodeside.

In a light-emitting device, although one light-emitting element may beformed over one substrate, a plurality of light-emitting elements may beformed over one substrate.

With a plurality of light-emitting elements as described above formedover one substrate, a lighting device in which elements are separated ora passive-matrix light-emitting device can be manufactured.

A light-emitting element may be formed over an electrode electricallyconnected to a thin film transistor (TFT), for example, which is formedover a substrate formed of glass, plastic, or the like, so that anactive matrix light-emitting device in which the TFT controls the driveof the light-emitting element can be manufactured.Note that there is no particular limitation on the structure of the TFT,which may be a staggered TFT or an inverted staggered TFT. In addition,crystallinity of a semiconductor used for the TFT is not particularlylimited either; an amorphous semiconductor or a crystallinesemiconductor may be used. In addition, a driver circuit formed in a TFTsubstrate may be formed with an n-type TFT and a p-type TFT, or witheither an n-type TFT or a p-type TFT.

Embodiment 6

In this embodiment is described one mode of a light-emitting elementhaving a structure in which a plurality of light-emitting units isstacked (hereinafter, also referred to as stacked-type element), withreference to FIG. 1B. This light-emitting element is a light-emittingelement including a plurality of light-emitting units between a firstelectrode and a second electrode. Each light-emitting unit can have thesame structure as the EL layer 103 which is described in Embodiment 5.In other words, the light-emitting element described in Embodiment 5 isa light-emitting element having one light-emitting unit while thelight-emitting element described in Embodiment 6 is a light-emittingelement having a plurality of light-emitting units.

In FIG. 1B, a first light-emitting unit 511 and a second light-emittingunit 512 are stacked between a first electrode 501 and a secondelectrode 502, and a charge generation layer 513 is provided between thefirst light-emitting unit 511 and the second light-emitting unit 512.The first electrode 501 and the second electrode 502 correspond,respectively, to the first electrode 101 and the second electrode 102 inEmbodiment 5, and materials described in Embodiment 5 can be used.Further, the structures of the first light-emitting unit 511 and thesecond light-emitting unit 512 may be the same or different.

The charge generation layer 513 contains a composite material of anorganic compound and a metal oxide. This composite material of anorganic compound and a metal oxide is the composite material describedin Embodiment 5, and contains an organic compound and a metal oxide suchas vanadium oxide, molybdenum oxide, or tungsten oxide. As the organiccompound, any of a variety of compounds such as aromatic aminecompounds, dibenzo[c,g]carbazole compounds, carbazole compounds,aromatic hydrocarbons, and high molecular compounds (oligomers,dendrimers, polymers, or the like) can be used. Note that as the organiccompound, the one having a hole mobility of 10⁻⁶ cm²/Vs or more as anorganic compound having a hole-transport property is preferably used.Further, other than these substances, any substance that has a propertyof transporting more holes than electrons may be used. Since a compositeof an organic compound and a metal oxide is excellent incarrier-injection property and carrier-transport property, low voltagedriving and low current driving can be achieved.

The charge generation layer 513 may be formed in such a way that a layercontaining the composite material of an organic compound and a metaloxide is combined with a layer containing another material, for example,with a layer that contains a compound selected from substances having anelectron-donating property and a compound having a highelectron-transport property. The charge generation layer 513 may beformed in such a way that a layer containing the composite material ofan organic compound and a metal oxide is combined with a transparentconductive film.

The charge generation layer 513 provided between the firstlight-emitting unit 511 and the second light-emitting unit 512 may haveany structure as far as electrons can be injected to a light-emittingunit on one side and holes can be injected to a light-emitting unit onthe other side when a voltage is applied between the first electrode 501and the second electrode 502. For example, in FIG. 1B, any layer can beused as the charge generation layer 513 as far as the layer injectselectrons into the first light-emitting unit 511 and holes into thesecond light-emitting unit 512 when a voltage is applied such that thevoltage of the first electrode is higher than that of the secondelectrode.

Although the light-emitting element having two light-emitting units isdescribed in this embodiment, the present invention can be similarlyapplied to a light-emitting element in which three or morelight-emitting units are stacked. By arrangement of a plurality oflight-emitting units, which are partitioned by the charge-generationlayer between a pair of electrodes, as in a light-emitting element inthis embodiment, light emission in a high luminance region can berealized with current density kept low, thus a light-emitting elementhaving a long lifetime can be realized. Further, in application tolighting devices, a voltage drop due to resistance of an electrodematerial can be reduced and accordingly light emission in a large areais possible. Moreover, a light-emitting device having low drivingvoltage and lower power consumption can be realized.

By making the light-emitting units emit light of different colors fromeach other, the light-emitting element can provide light emission of adesired color as a whole. For example, by forming a light-emittingelement having two light-emitting units such that the emission color ofthe first light-emitting unit and the emission color of the secondlight-emitting unit are complementary colors, the light-emitting elementcan provide white light emission as a whole. Note that the word“complementary” means color relationship in which an achromatic color isobtained when colors are mixed. In other words, when lights obtainedfrom substances which emit light of complementary colors are mixed,white emission can be obtained. Further, the same can be applied to alight-emitting element having three light-emitting units. For example,the light-emitting element as a whole can provide white light emissionwhen the emission color of the first light-emitting unit is red, theemission color of the second light-emitting unit is green, and theemission color of the third light-emitting unit is blue.

Since a light-emitting element in this embodiment includes adibenzo[c,g]carbazole compound described in Embodiment 2, thelight-emitting element can be a light-emitting element having highemission efficiency, a light-emitting element having low drivingvoltage, or a light-emitting element having a long lifetime. Inaddition, since light emission with high color purity which is derivedfrom the emission center substance can be obtained from thelight-emitting unit including the dibenzo[c,g]carbazole compound, coloradjustment of the light-emitting element as a whole is easy.

Note that this embodiment can be combined with any of the otherembodiments as appropriate.

Embodiment 7

In this embodiment, a light-emitting device using a light-emittingelement including a dibenzo[c,g]carbazole compound described inEmbodiment 2 (light-emitting element described in Embodiment 1) isdescribed.

In this embodiment, the light-emitting device using a light-emittingelement including a dibenzo[c,g]carbazole compound described inEmbodiment 2 (light-emitting element described in Embodiment 1) isdescribed with reference to FIGS. 3A and 3B. Note that FIG. 3A is a topview illustrating the light-emitting device and FIG. 3B is across-sectional view of FIG. 3A taken along the lines A-B and C-D. Thislight-emitting device includes a driver circuit portion (source linedriver circuit) 601, a pixel portion 602, and a driver circuit portion(gate line driver circuit) 603, which are to control light emission ofthe light-emitting element and illustrated with dotted lines. Moreover,a reference numeral 604 denotes a sealing substrate; 625, a desiccant;605, a sealing material; and 607, a space surrounded by the sealingmaterial 605.

Reference numeral 608 denotes a wiring for transmitting signals to beinputted into the source line driver circuit 601 and the gate linedriver circuit 603 and receiving signals such as a video signal, a clocksignal, a start signal, and a reset signal from an FPC (flexible printedcircuit) 609 serving as an external input terminal. Although only theFPC is illustrated here, a printed wiring board (PWB) may be attached tothe FPC. The light-emitting device in the present specificationincludes, in its category, not only the light-emitting device itself butalso the light-emitting device provided with the FPC or the PWB.

Next, a cross-sectional structure is described with reference to FIG.3B. The driver circuit portion and the pixel portion are formed over anelement substrate 610; the source line driver circuit 601, which is adriver circuit portion, and one of the pixels in the pixel portion 602are illustrated here

As the source line driver circuit 601, a CMOS circuit in which ann-channel TFT 623 and a p-channel TFT 624 are combined is formed. Inaddition, the driver circuit may be formed with any of a variety ofcircuits such as a CMOS circuit, a PMOS circuit, or an NMOS circuit.Although a driver integrated type in which the driver circuit is formedover the substrate is illustrated in this embodiment, the driver circuitmay not necessarily be formed over the substrate, and the driver circuitcan be formed outside, not over the substrate.

The pixel portion 602 includes a plurality of pixels including aswitching TFT 611, a current controlling TFT 612, and a first electrode613 electrically connected to a drain of the current controlling TFT612. Note that to cover an end portion of the first electrode 613, aninsulator 614 is formed, for which a positive type photosensitiveacrylic resin film is used here.

In order to improve coverage, the insulator 614 is formed to have acurved surface with curvature at its upper or lower end portion. Forexample, in the case where positive photosensitive acrylic is used for amaterial of the insulator 614, only the upper end portion of theinsulator 614 preferably has a curved surface with a curvature radius(0.2 μm to 3 μm). As the insulator 614, either a negative photosensitiveresin or a positive photosensitive resin can be used.

An EL layer 616 and a second electrode 617 are formed over the firstelectrode 613. Here, as a material used for the first electrode 613functioning as an anode, a material having a high work function ispreferably used. For example, a single-layer film of an ITO film, anindium tin oxide film containing silicon, an indium oxide filmcontaining zinc oxide at 2 wt % to 20 wt %, a titanium nitride film, achromium film, a tungsten film, a Zn film, a Pt film, or the like, astack of a titanium nitride film and a film containing aluminum as itsmain component, a stack of three layers of a titanium nitride film, afilm containing aluminum as its main component, and a titanium nitridefilm, or the like can be used. Note that when the stacked structure isused, the first electrode 613 has low resistance as a wiring, forms afavorable ohmic contact, and can function as an anode.

In addition, the EL layer 616 is formed by any of a variety of methodssuch as an evaporation method using a shadow mask, an inkjet method, anda spin coating method. The EL layer 616 includes a dibenzo[c,g]carbazolecompound described in Embodiment 2. Further, another material includedin the EL layer 616 may be a low molecular compound or a high molecularcompound (which may be an oligomer and a dendrimer).

As a material used for the second electrode 617, which is formed overthe EL layer 616 and functions as a cathode, a material having a lowwork function (e.g., Al, Mg, Li, Ca, or an alloy or compound thereof,such as MgAg, MgIn, or AlLi) is preferably used. In the case where lightgenerated in the EL layer 616 passes through the second electrode 617, astack of a thin metal film and a transparent conductive film (e.g., ITO,indium oxide containing zinc oxide at 2 wt % to 20 wt %, indium tinoxide containing silicon, or zinc oxide (ZnO)) is preferably used forthe second electrode 617.

Note that the light-emitting element is formed with the first electrode613, the EL layer 616, and the second electrode 617. The light-emittingelement has the structure described in Embodiment 5. In thelight-emitting device of this embodiment, the pixel portion, whichincludes a plurality of light-emitting elements, may include both thelight-emitting element described in Embodiment 1 with the structuredescribed in Embodiment 5 or 6 and a light-emitting element with astructure other than those.

Further, the sealing substrate 604 is attached to the element substrate610 with the sealing material 605, so that a light-emitting element 618is provided in the space 607 surrounded by the element substrate 610,the sealing substrate 604, and the sealing material 605. The space 607may be filled with filler, and may be filled with an inert gas (such asnitrogen or argon), or the sealing material 605.

An epoxy-based resin or glass frit is preferably used for the sealingmaterial 605. It is preferable that such a material do not transmitmoisture or oxygen as much as possible. As the sealing substrate 604, aglass substrate, a quartz substrate, or a plastic substrate formed offiberglass reinforced plastic (FRP), polyvinyl fluoride (PVF),polyester, acrylic, or the like can be used.

As described above, the light-emitting device using a light-emittingelement including a dibenzo[c,g]carbazole compound described inEmbodiment 2 (light-emitting element described in Embodiment 1) can beobtained.

A light-emitting element including a dibenzo[c,g]carbazole compounddescribed in Embodiment 2 (light-emitting element described inEmbodiment 1) is used in the light-emitting device in this embodiment,and thus a light-emitting device having favorable characteristics can beobtained. Specifically, since a dibenzo[c,g]carbazole compound describedin Embodiment 2 has a large energy gap and high triplet excitationenergy and can suppress energy transfer from a light-emitting substance,a light-emitting element having high emission efficiency can beprovided, and accordingly a light-emitting device having reduced powerconsumption can be provided. In addition, a light-emitting elementhaving low driving voltage can be provided, and accordingly alight-emitting device having low driving voltage can be provided.Further, since a light-emitting element using a dibenzo[c,g]carbazolecompound described in Embodiment 2 (light-emitting element described inEmbodiment 1) is a light-emitting element having a long lifetime, alight-emitting device with high reliability can be provided.

Although an active matrix light-emitting device is described in thisembodiment as described above, a passive matrix light-emitting devicemay be manufactured. FIGS. 4A and 4B illustrate a passive matrixlight-emitting device manufactured using the present invention. FIG. 4Ais a perspective view of the light-emitting device, and FIG. 4B is across-sectional view taken along line X-Y in FIG. 4A. In FIGS. 4A and4B, over a substrate 951, an EL layer 955 is provided between anelectrode 952 and an electrode 956. An end portion of the electrode 952is covered with an insulating layer 953. In addition, a partition layer954 is provided over the insulating layer 953. The sidewalls of thepartition layer 954 are aslope such that the distance between bothsidewalls is gradually narrowed toward the surface of the substrate. Inother words, a cross section taken along the direction of the short sideof the partition wall layer 954 is trapezoidal, and the lower side (aside which is in the same direction as a plane direction of theinsulating layer 953 and in contact with the insulating layer 953) isshorter than the upper side (a side which is in the same direction asthe plane direction of the insulating layer 953 and not in contact withthe insulating layer 953). The partition layer 954 thus provided canprevent defects in the light-emitting element due to static electricityor the like. The passive matrix light-emitting device can also be drivenwhile power consumption is kept low, by including a light-emittingelement described in Embodiment 1 which is capable of operating at lowvoltage and includes a dibenzo[c,g]carbazole compound described inEmbodiment 2. In addition, the light-emitting device can be driven whilepower consumption is kept low, by including a light-emitting elementdescribed in Embodiment 1 which includes a dibenzo[c,g]carbazolecompound described in Embodiment 2 and accordingly has high emissionefficiency. Further, the light-emitting device can have high reliabilityby including a light-emitting element described in Embodiment 1 whichincludes a dibenzo[c,g]carbazole compound described in Embodiment 2.

Embodiment 8

In this embodiment, an example in which a light-emitting element using adibenzo[c,g]carbazole compound described in Embodiment 2 (light-emittingelement described in Embodiment 1) is used for a lighting device isdescribed with reference to FIGS. 5A and 5B. FIG. 5B is a top view ofthe lighting device, and FIG. 5A is a cross-sectional view taken alongthe line E-F in FIG. 5B.

In the lighting device in this embodiment, a first electrode 401 isformed over a substrate 400 which is a support and has alight-transmitting property. The first electrode 401 corresponds to thefirst electrode 101 in Embodiment 5.

An auxiliary electrode 402 is provided over the first electrode 401.Since light emission is extracted through the first electrode 401 sidein the example given in this embodiment, the first electrode 401 isformed using a material having a light-transmitting property. Theauxiliary electrode 402 is provided in order to compensate for the lowconductivity of the material having a light-transmitting property, andhas a function of suppressing luminance unevenness in a light emissionsurface due to voltage drop caused by the high resistance of the firstelectrode 401. The auxiliary electrode 402 is formed using a materialhaving at least higher conductivity than the material of the firstelectrode 401, and is preferably formed using a material having highconductivity such as aluminum. Note that surfaces of the auxiliaryelectrode 402 other than a portion thereof in contact with the firstelectrode 401 are preferably covered with an insulating layer. With sucha structure, light emission over the upper portion of the auxiliaryelectrode 402, which cannot be extracted, can be suppressed, so that areduction in power efficiency due to reactive current can be suppressed.Note that a pad 412 for applying a voltage to a second electrode 404 maybe formed at the same time as the formation of the auxiliary electrode402.

An EL layer 403 is formed over the first electrode 401 and the auxiliaryelectrode 402. The EL layer 403 corresponds to a structure of the ELlayer 103 in Embodiment 5 or a structure combining the light-emittingunits 511 and 512 and the charge generation layer 513. See theexplanations of these structures. Note that the EL layer 403 ispreferably formed to be slightly larger than the first electrode 401when seen from above, in which case the EL layer 403 can also serve asan insulating layer that suppresses a short circuit between the firstelectrode 401 and the second electrode 404.

The second electrode 404 is formed to cover the EL layer 403. The secondelectrode 404 corresponds to the second electrode 102 in Embodiment 5and has a similar structure. In this embodiment, it is preferable thatthe second electrode 404 be formed using a material having highreflectance because light emission is extracted through the firstelectrode 401 side. In this embodiment, the second electrode 404 isconnected to the pad 412, whereby voltage is applied.

As described above, the lighting device described in this embodimentincludes a light-emitting element including the first electrode 401, theEL layer 403, and the second electrode 404 (and the auxiliary electrode402). Since the light-emitting element is a light-emitting element withhigh emission efficiency, the lighting device in this embodiment can bea lighting device having low power consumption. Further, since thelight-emitting element is a light-emitting element having low drivingvoltage, the lighting device in this embodiment can be a lighting devicehaving low power consumption. Furthermore, since the light-emittingelement is a light-emitting element having high reliability, thelighting device in this embodiment can be a lighting device having highreliability.

The light-emitting element having the above structure is fixed to asealing substrate 407 with sealing materials 405 and 406 and sealing isperformed, whereby the lighting device is completed. It is possible touse only either the sealing material 405 or the sealing material 406. Inaddition, the inner sealing material 406 can be mixed with a desiccantwhich enables moisture to be adsorbed, increasing reliability.

When extended to the outside of the sealing materials 405 and 406, thepad 412, the first electrode 401, and the auxiliary electrode 402 caneach partly serve as external input terminal. An IC chip 420 mountedwith a converter or the like may be provided over the external inputterminals.

As described above, since the lighting device described in thisembodiment includes a light-emitting element including adibenzo[c,g]carbazole compound described in Embodiment 2 (light-emittingelement described in Embodiment 1) as an EL element, the lighting devicecan be a lighting device having low power consumption, a lighting devicewith low driving voltage, or a lighting device with high reliability.

Embodiment 9

In this embodiment, examples of an electronic device including alight-emitting element including a dibenzo[c,g]carbazole compounddescribed in Embodiment 2 (light-emitting element described inEmbodiment 1) are described. A light-emitting element including adibenzo[c,g]carbazole compound described in Embodiment 2 (light-emittingelement described in Embodiment 1) is a light-emitting element havingfavorable emission efficiency and reduced power consumption.Accordingly, an electronic device described in this embodiment can be anelectronic device including a light-emitting portion having reducedpower consumption. Further, since a light-emitting element including adibenzo[c,g]carbazole compound described in Embodiment 2 (light-emittingelement described in Embodiment 1) is a light-emitting element havinglow driving voltage, an electronic device described in this embodimentcan be an electronic device having low driving voltage. Furthermore,since a light-emitting element including a dibenzo[c,g]carbazolecompound described in Embodiment 2 (light-emitting element described inEmbodiment 1) is a light-emitting element having a long lifetime, anelectronic device described in this embodiment can be an electronicdevice having high reliability.

Examples of the electronic devices to which the above light-emittingelement is applied are television sets (also referred to as televisionsor television receivers), monitors of computers or the like, camerassuch as digital cameras or digital video cameras, digital photo frames,mobile phone sets (also referred to as mobile phones or mobile phonedevices), portable game machines, portable information terminals, audioreproducing devices, large-sized game machines such as pachinkomachines, and the like. Specific examples of these electronic devicesare described below.

FIG. 6A illustrates an example of a television set. In the televisionset, a display portion 7103 is incorporated in a housing 7101. Inaddition, here, the housing 7101 is supported by a stand 7105. Thedisplay portion 7103 enables display of images and includeslight-emitting elements arranged in a matrix, each of which is alight-emitting element including a dibenzo[c,g]carbazole compounddescribed in Embodiment 2 (light-emitting element described inEmbodiment 1). The light-emitting elements can have high emissionefficiency. Further, the light-emitting elements can have low drivingvoltage. Furthermore, the light-emitting elements can have a longlifetime. Accordingly, the television device that has the displayportion 7103 including the light-emitting elements can be a televisiondevice having reduced power consumption. Further, the television devicecan be a television device having low driving voltage. Furthermore, thetelevision device can be a television device having high reliability.

Operation of the television set can be performed with an operationswitch of the housing 7101 or a separate remote control 7110. Withoperation keys 7109 of the remote control 7110, channels and volume canbe controlled and images displayed on the display portion 7103 can becontrolled. Furthermore, the remote control 7110 may be provided with adisplay portion 7107 for displaying data output from the remote control7110.

Note that the television set is provided with a receiver, a modem, andthe like. With the receiver, a general television broadcast can bereceived. Furthermore, when the television set is connected to acommunication network by wired or wireless connection via the modem,one-way (from a transmitter to a receiver) or two-way (between atransmitter and a receiver, between receivers, or the like) datacommunication can be performed.

FIG. 6B illustrates a computer having a main body 7201, a housing 7202,a display portion 7203, a keyboard 7204, an external connection port7205, a pointing device 7206, and the like. Note that this computer ismanufactured by using light-emitting elements arranged in a matrix, eachof which is a light-emitting element including a dibenzo[c,g]carbazolecompound described in Embodiment 2 (light-emitting element described inEmbodiment 1). The light-emitting elements can have high emissionefficiency. Further, the light-emitting elements can have low drivingvoltage. Furthermore, the light-emitting elements can have a longlifetime. Accordingly, the computer that has the display portion 7203including the light-emitting elements can be a computer having reducedpower consumption. Further, the computer can be a computer having lowdriving voltage. Furthermore, the computer can be a computer having highreliability.

FIG. 6C illustrates a portable game machine having two housings, ahousing 7301 and a housing 7302, which are connected with a jointportion 7303 so that the portable game machine can be opened or folded.A display portion 7304 including light-emitting elements arranged in amatrix which are described in Embodiment 1 and is incorporated in thehousing 7301, and a display portion 7305 is incorporated in the housing7302. A display portion 7304 is incorporated in the housing 7301, and adisplay portion 7305 is incorporated in the housing 7302. In addition,the portable game machine illustrated in FIG. 6C includes a speakerportion 7306, a recording medium insertion portion 7307, an LED lamp7308, input means (an operation key 7309, a connection terminal 7310, asensor 7311 (a sensor having a function of measuring force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, current,voltage, electric power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared rays), and a microphone 7312), and thelike. It is needless to say that the structure of the portable gamemachine is not limited to the above as far as the display portionincluding light-emitting elements arranged in a matrix, each of which isa light-emitting element including a dibenzo[c,g]carbazole compounddescribed in Embodiment 2 (light-emitting element described inEmbodiment 1) is used as at least either the display portion 7304 or thedisplay portion 7305, or both, and the structure can include otheraccessories as appropriate. The portable game machine illustrated inFIG. 6C has a function of reading out a program or data stored in astorage medium to display it on the display portion, and a function ofsharing information with another portable game machine by wirelesscommunication. The portable game machine illustrated in FIG. 6C can havea variety of functions without limitation to the above. Since thelight-emitting elements used in the display portion 7304 have highemission efficiency, the portable game machine including theabove-described display portion 7304 can be a portable game machinehaving reduced power consumption. Since the light-emitting elements usedin the display portion 7304 has low driving voltage, the portable gamemachine can also be a portable game machine having low driving voltage.Furthermore, since the light-emitting elements used in the displayportion 7304 has high reliability, the portable game machine can also bea portable game machine having high reliability.

FIG. 6D illustrates an example of a mobile phone. A mobile phone 7400 isprovided with a display portion 7402 incorporated in a housing 7401,operation buttons 7403, an external connection port 7404, a speaker7405, a microphone 7406, and the like. Note that the mobile phone 7400is manufactured using the light-emitting device for the display portion7402. Note that the cellular phone 7400 has the display portion 7402including light-emitting elements arranged in a matrix, each of which isa light-emitting element including a dibenzo[c,g]carbazole compounddescribed in Embodiment 2 (light-emitting element described inEmbodiment 1). The light-emitting elements can have high emissionefficiency. Further, the light-emitting elements can have low drivingvoltage. Furthermore, the light-emitting elements can have a longlifetime. Accordingly, the cellular phone that has the display portion7402 including the light-emitting elements can be a cellular phonehaving reduced power consumption. Further, the mobile phone can be amobile phone having low driving voltage. Furthermore, the mobile phonecan be a mobile phone having high reliability.

When the display portion 7402 of the mobile phone 7400 illustrated inFIG. 6D is touched with a finger or the like, data can be input to themobile phone. In this case, operations such as making a call andcreating mail can be performed by touching the display portion 7402 witha finger or the like.

There are mainly three screen modes of the display portion 7402. Thefirst mode is a display mode mainly for displaying images. The secondmode is an input mode mainly for inputting data of a character and thelike. The third mode is a display-and-input mode in which two modes ofthe display mode and the input mode are combined.

For example, in the case of making a call or creating an e-mail, a textinput mode mainly for inputting a character is selected for the displayportion 7402 so that a character displayed on the screen can be input.In this case, it is preferable to display a keyboard or number buttonson almost the entire screen of the display portion 7402.

When a detection device including a sensor for detecting inclination,such as a gyroscope or an acceleration sensor, is provided inside themobile phone, display on the screen of the display portion 7402 can beautomatically switched by determining the orientation of the mobilephone (whether the mobile phone is placed horizontally or vertically fora landscape mode or a portrait mode).

The screen modes are switched by touching the display portion 7402 oroperating the operation buttons 7403 of the housing 7401. The screenmodes can also be switched depending on the kind of image displayed onthe display portion 7402. For example, when a signal of an imagedisplayed on the display portion is a signal of moving image data, thescreen mode is switched to the display mode. When the signal is a signalof text data, the screen mode is switched to the input mode.

Moreover, in the input mode, when input by touching the display portion7402 is not performed for a certain period while a signal detected by anoptical sensor in the display portion 7402 is detected, the screen modemay be controlled so as to be switched from the input mode to thedisplay mode.

The display portion 7402 may function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken when thedisplay portion 7402 is touched with the palm or the finger, wherebypersonal authentication can be performed. Further, by providing abacklight or a sensing light source which emits near-infrared light inthe display portion, an image of a finger vein, a palm vein, or the likecan be taken.

Note that the structure described in this embodiment can be combinedwith any of the structures described in Embodiments 1 to 8 asappropriate.

As described above, the application range of the light-emitting devicehaving a light-emitting element including a dibenzo[c,g]carbazolecompound described in Embodiment 2 (light-emitting element described inEmbodiment 1) is wide so that this light-emitting device can be appliedto electronic devices in a variety of fields. By use of a light-emittingelement including a dibenzo[c,g]carbazole compound described inEmbodiment 2, an electronic device having reduced power consumption canbe obtained. In addition, an electronic device having low drivingvoltage can be obtained.

FIG. 7 illustrates an example of a liquid crystal display device using alight-emitting element including a dibenzo[c,g]carbazole compounddescribed in Embodiment 2 (light-emitting element described inEmbodiment 1) for a backlight. The liquid crystal display deviceillustrated in FIG. 7 includes a housing 901, a liquid crystal layer902, a backlight 903, and a housing 904. The liquid crystal layer 902 isconnected to a driver IC 905. A light-emitting element including adibenzo[c,g]carbazole compound described in Embodiment 2 (light-emittingelement described in Embodiment 1) is used in the backlight 903, towhich a current is supplied through a terminal 906.

A light-emitting element including a dibenzo[c,g]carbazole compounddescribed in Embodiment 2 (light-emitting element described inEmbodiment 1) is used for the backlight of the liquid crystal displaydevice, and thus a backlight having reduced power consumption can beobtained. In addition, use of a light-emitting element including adibenzo[c,g]carbazole compound described in Embodiment 2 enablesmanufacture of a planar-emission lighting device and further alarger-area planar-emission lighting device; therefore, the backlightcan be a larger-area backlight, and the liquid crystal display devicecan also be a larger-area device. Furthermore, the backlight using alight-emitting element including a dibenzo[c,g]carbazole compounddescribed in Embodiment 2 (light-emitting element described inEmbodiment 1) can be thinner than a conventional one; accordingly, thedisplay device can also be thinner.

FIG. 8 illustrates an example in which a light-emitting elementincluding a dibenzo[c,g]carbazole compound described in Embodiment 2(light-emitting element described in Embodiment 1) is used for a tablelamp which is a lighting device. The table lamp illustrated in FIG. 8includes a housing 2001 and a light source 2002, and the light-emittingdevice described in Embodiment 8 is used for the light source 2002.

FIG. 9 illustrates an example in which a light-emitting elementincluding a dibenzo[c,g]carbazole compound described in Embodiment 2(light-emitting element described in Embodiment 1) is used for an indoorlighting device 3001. Since a light-emitting element including adibenzo[c,g]carbazole compound described in Embodiment 2 has reducedpower consumption, a lighting device that has reduced power consumptioncan be obtained. Further, since a light-emitting element including adibenzo[c,g]carbazole compound described in Embodiment 2 can have alarge area, the light-emitting element can be used for a large-arealighting device. Furthermore, since a light-emitting element including adibenzo[c,g]carbazole compound described in Embodiment 2 is thin, thelight-emitting element can be used for a lighting device having areduced thickness.

A light-emitting element including a dibenzo[c,g]carbazole compounddescribed in Embodiment 2 (light-emitting element described inEmbodiment 1) can also be used for an automobile windshield ordashboard. One mode in which the light-emitting elements including adibenzo[c,g]carbazole compound described in Embodiment 1 are used for anautomobile windshield and an automobile dashboard is illustrated in FIG.10. Display regions 5000 to 5005 each include a light-emitting elementincluding a dibenzo[c,g]carbazole compound described in Embodiment 2.

The display region 5000 and the display region 5001 are display deviceswhich are provided in the automobile windshield and in which thelight-emitting elements including a dibenzo[c,g]carbazole compounddescribed in Embodiment 2 (i.e., each of which is a light-emittingelement described in Embodiment 1) are incorporated. The light-emittingelements including a dibenzo[c,g]carbazole compound described inEmbodiment 2 can be formed into so-called see-through display devices,through which the opposite side can be seen, by including a firstelectrode and a second electrode formed with electrodes having alight-transmitting property. Such see-through display devices can beprovided even in the automobile windshield, without hindering thevision. Note that in the case where a transistor for driving isprovided, a transistor having a light-transmitting property, such as anorganic transistor using an organic semiconductor material or atransistor using an oxide semiconductor, is preferably used

The display region 5002 is a display device which is provided in apillar portion and in which a light-emitting element including adibenzo[c,g]carbazole compound described in Embodiment 2 (light-emittingelement described in Embodiment 1) is incorporated. The display region5002 can compensate for the view hindered by the pillar portion byshowing an image taken by an imaging element provided in the automobilebody. Similarly, the display region 5003 provided in the dashboard cancompensate for the view hindered by the automobile body by showing animage taken by an imaging element provided in the outside of theautomobile body, which leads to elimination of blind areas andenhancement of safety. Showing an image so as to compensate for the areawhich a driver cannot see, makes it possible for the driver to confirmsafety easily and comfortably.

The display region 5004 and the display region 5005 can provide avariety of kinds of information such as navigation data, a speedometer,a tachometer, a mileage, a fuel meter, a gearshift indicator, andair-condition setting. The content or layout of the display can bechanged freely by a user as appropriate. Further, such information canalso be shown by the display regions 5000 to 5003. Note that the displayregions 5000 to 5005 can also be used as lighting devices.

A light-emitting element including a dibenzo[c,g]carbazole compounddescribed in Embodiment 2 (light-emitting element described inEmbodiment 1) can be a light-emitting element having low driving voltageor a light-emitting element having low power consumption. Accordingly,even when a number of large screens such as display regions 5000 to 5005are provided, load on a battery can be reduced, which providescomfortable use. The light-emitting device and the lighting device eachusing a light-emitting element including a dibenzo[c,g]carbazolecompound described in Embodiment 2 can be suitably used as an in-vehiclelight-emitting device or lighting device.

Example 1

In this example, a synthesis method of7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA), which is a dibenzo[c,g]carbazole compoundrepresented by the general formula (G1) described in Embodiment 2, isdescribed in detail.

Step 1: Synthesis of 5,6,8,9-Tetrahydro-7H-dibenzo[c,g]carbazole

In a 100 mL three-neck flask were placed 1.0 g (20 mmol) of hydrazinemonohydrate and 14 mL ethanol. To this solution in an ice bath was addeddropwise 2.2 mL of a 1.7 M acetic acid aqueous solution with a droppingfunnel. To this solution were added dropwise 10 g (68 mmol) ofβ-tetralone dissolved in 10 mL ethanol with a dropping funnel. Thismixture was stirred at 80° C. for 7 hours, whereby a solid wasprecipitated. After the stirring, this mixture was added to about 50 mLof water and the mixture was stirred at room temperature for 30 minutes.After the stirring, this mixture was suction-filtered to collect asolid. Methanol/water in a 1:1 ratio was added to the collected solidand the mixture was irradiated with ultrasonic waves, and a solid waswashed. After the washing, this mixture was suction-filtered and a solidwas collected, giving 3.5 g of a yellow powder in a yield of 63%. Areaction scheme (a-1) of Step 1 is illustrated below.

Step 2: Synthesis of 7H-Dibenzo[c,g]carbazole

In a 200 mL three-neck flask were placed 6.2 g of chloranil (25 mmol),40 mL of xylene, and 3.5 g (12 mmol) of5,6,8,9-tetrahydro-7H-benzo[c,g]carbazole suspended in 20 mL of xylene.This mixture was refluxed at 150° C. for 4 hours under a nitrogenstream. After reaction, this mixture cooled to room temperature,precipitating a solid. The precipitated solid was removed by suctionfiltration and a filtrate was obtained. The obtained filtrate waspurified by silica gel column chromatography (developing solvent:toluene/hexane in a 2:1 ratio) to give a red solid. Recrystallization ofthe obtained solid from toluene/hexane gave pale-red needle-likecrystals. The obtained crystals were again recrystallized fromtoluene/hexane, so that 2.5 g of white needle-like crystals wereobtained in 78% yield. A reaction scheme (b-1) of Step 2 is illustratedbelow.

Step 3: Synthesis of7-[4-(10-Phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole (cgDBCzPA)

In a 100 mL three-neck flask were placed 2.3 g (5.6 mmol) of9-(4-bromophenyl)-10-phenylanthracene, 1.5 g (5.6 mol) of7H-dibenzo[c,g]carbazole, and 1.2 g (12 mmol) of sodium tert-butoxide.After the air in the flask was replaced with nitrogen, to this mixturewere added 30 mL of toluene and 2.8 mL of tri-(tert-butyl)phosphine (a10 wt % hexane solution). This mixture was degassed by being stirredwhile the pressure was reduced. After the degassing, 0.16 g (0.28 mmol)of bis(dibenzylideneacetone)palladium(0) was added to this mixture. Thismixture was stirred at 110° C. for 17 hours under a nitrogen stream, sothat a solid was precipitated. The precipitated solid was removed bysuction filtration. The collected solid was dissolved in about 30 mL ofhot toluene, and this solution was suction-filtered through Celite(produced by Wako Pure Chemical Industries, Ltd., Catalog No.531-16855), alumina, and Florisil (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 540-00135). A solid obtained byconcentration of the filtrate was recrystallized from toluene/hexane togive 2.3 g of a pale yellow powder, which was the object of thesynthesis, in a yield of 70%. A reaction scheme (c-1) of Step 3 isillustrated below.

By a train sublimation method, 2.3 g of the obtained pale yellow powderysolid was purified by sublimation. In the sublimation purification,cgDBCzPA was heated at 310° C. under a pressure of 3.6 Pa with a flowrate of argon at 6.0 mL/min. After the sublimation purification, 2.1 gof a pale yellow solid of cgDBCzPA was recovered in 91% yield.

The obtained substance was measured by ¹H NMR. The measurement data areshown below.

¹H NMR (CDCl₃, 300 MHz): δ=7.38-7.67 (m, 11H), 7.72-7.89 (m, 12H), 7.96(d, J=8.7 Hz, 2H), 8.10 (d, J=7.2 Hz, 2H), 9.31 (d, J₁=8.1 Hz, 2H)

In addition, FIGS. 11A and 11B are ¹H-NMR charts. The measurementresults show that7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA) represented by the above structural formula wasobtained.

Next, absorption and emission spectra of cgDBCzPA in a toluene solutionof cgDBCzPA are shown in FIG. 12A, and absorption and emission spectraof a thin film of cgDBCzPA are shown in FIG. 12B. The absorption spectrawere measured using an ultraviolet-visible light spectrophotometer (V550type manufactured by Japan Spectroscopy Corporation). A toluene solutionof cgDBCzPA was put in a quartz cell and an absorption spectrum ofcgDBCzPA in the toluene solution was measured. From this absorptionspectrum, an absorption spectrum of the toluene solution measured withthe quartz cell was subtracted, and the resultant value was shown in thedrawing. In addition, as for the absorption spectrum of the thin film, asample was prepared by evaporation of cgDBCzPA over a quartz substrate,and the absorption spectrum obtained by subtraction of an absorptionspectrum of quartz from the absorption spectrum of this sample is shownin the drawing. As in the measurements of the absorption spectra, anultraviolet-visible spectrophotometer (V550, manufactured by JASCOCorporation) was used for the measurements of the emission spectra. Theemission spectrum of cgDBCzPA in a toluene solution of cgDBCzPA wasmeasured with the toluene solution of cgDBCzPA put in a quartz cell, andthe emission spectrum of the thin film was measured with a sampleprepared by evaporation of cgDBCzPA over a quartz substrate. These showthat the maximum absorption wavelengths of cgDBCzPA in the toluenesolution of cgDBCzPA were around 396 nm, around 368 nm, around 351 nm,around 306 nm, and around 252 nm and that the maximum emissionwavelengths thereof were around 417 nm and around 432 nm (an excitationwavelength of 369 nm). These also show that the maximum absorptionwavelengths of the thin film were around 402 nm, around 375 nm, around357 nm, around 343 nm, around 306 nm, around 268 nm, around 252 nm, andaround 221 nm and that the largest maximum emission wavelength thereofwas around 442 nm (an excitation wavelength of 402 nm).

Further, the ionization potential of a thin film of cgDBCzPA wasmeasured by a photoelectron spectrometer (AC-2, manufactured by RikenKeiki, Co., Ltd.) in the air. The obtained value of the ionizationpotential was converted to a negative value, revealing that the HOMOlevel of cgDBCzPA was −5.72 eV. From the data of the absorption spectraof the thin film in FIGS. 12A and 12B, the absorption edge of cgDBCzPA,which was obtained from a Tauc plot with an assumption of directtransition, was 2.95 eV. Therefore, the optical energy gap of cgDBCzPAin the solid state was estimated at 2.95 eV; from the values of the HOMOlevel obtained above and this energy gap, the LUMO level of cgDBCzPA wasable to be estimated at −2.77 eV. It was thus found that cgDBCzPA had awide energy gap of 2.95 eV in the solid state.

The oxidation characteristics and reduction characteristics of cgDBCzPAwere measured. These were examined by cyclic voltammetry (CV)measurements. An electrochemical analyzer (ALS model 600A or 600C,manufactured by BAS Inc.) was used for the measurements.

Further, as for a solution used for the CV measurements, dehydrateddimethylformamide (DMF, manufactured by Sigma-Aldrich Inc., 99.8%,Catalog No. 22705-6) was used as a solvent, and tetra-n-butylammoniumperchlorate (n-Bu₄NClO₄, manufactured by Tokyo Chemical Industry Co.,Ltd., Catalog No. T0836), which was a supporting electrolyte, wasdissolved in the solvent such that the concentration was 100 mmol/L.Further, the object to be measured was dissolved in the solvent suchthat the concentration was 2 mmol/L. A platinum electrode (PTE platinumelectrode, manufactured by BAS Inc.) was used as a working electrode, aplatinum electrode (Pt counter electrode for VC-3 (5 cm), manufacturedby BAS Inc.) was used as an auxiliary electrode, and an Ag/Ag⁺ electrode(RE-5 reference electrode for nonaqueous solvent, manufactured by BASInc.) was used as a reference electrode. Note that the measurements wereconducted at room temperature (20 to 25° C.). The scan rate was set to0.1 V/s through the CV measurements.

In the measurements of the oxidation characteristics, one cycle wasscanning in which the potential of the working electrode with respect tothe reference electrode was changed from 0.05 V to 0.83 V and thenchanged from 0.83 V to 0.05 V, and 100-cycle measurements wereperformed. Measurement results were shown in FIG. 13A.

The measurement results revealed that cgDBCzPA showed propertieseffective against repetition of redox reactions between an oxidizedstate and a neutral state without large variations in oxidation peakeven after the 100-cycle measurements.

In the measurements of the reduction characteristics, one cycle wasscanning in which the potential of the working electrode with respect tothe reference electrode was changed from −1.50 V to −2.30 V and thenchanged from −2.30 V to −1.50 V, and 100-cycle measurements wereperformed. Measurement results were shown in FIG. 13B.

The measurement results revealed that cgDBCzPA showed propertieseffective against repetition of redox reactions between a reduced stateand a neutral state without large variations in reduction peak evenafter the 100 cycles in the measurements.

Further, the HOMO and LUMO levels of cgDBCzPA were calculated also fromthe CV measurement results.

First, the potential energy of the reference electrode with respect tothe vacuum level used was found to be −4.94 eV. According to themeasurement results of the oxidation characteristics of cgDBCzPA, theoxidation peak potential E_(pa) was 0.81 V and the reduction peakpotential E_(pc) was 0.69 V. Therefore, a half-wave potential (anintermediate potential between E_(pa) and E_(pc)) can be determined at0.75 V. This means that cgDBCzPA is oxidized by an electric energy of0.75 [V vs. Ag/Ag⁺], and this energy corresponds to the HOMO level.Here, since the potential energy of the reference electrode, which wasused in this example, with respect to the vacuum level is −4.94 [eV] asdescribed above, the HOMO level of cgDBCzPA was found to be as follows:−4.94−0.75=−5.69 [eV]. According to the measurement results of thereduction characteristics of cgDBCzPA, the oxidation peak potentialE_(pc) was −2.25 V and the reduction peak potential E_(pa) was −2.16 V.Therefore, a half-wave potential (an intermediate potential betweenE_(pc) and E_(pa)) can be calculated at −2.21 V. This means thatcgDBCzPA is reduced by an electric energy of −2.21 [V vs. Ag/Ag⁺], andthis energy corresponds to the LUMO level. Here, since the potentialenergy of the reference electrode, which was used in this example, withrespect to the vacuum level is −4.94 [eV] as described above, the LUMOlevel of cgDBCzPA was found to be as follows: −4.94−(−2.21)=−2.74 [eV].

Note that the potential energy of the reference electrode (Ag/Ag⁺electrode) with respect to the vacuum level corresponds to the Fermilevel of the Ag/Ag⁺ electrode, and should be calculated from a valueobtained by measuring a substance whose potential energy with respect tothe vacuum level is known, with the use of the reference electrode(Ag/Ag⁺ electrode).

How the potential energy (eV) of the reference electrode (Ag/Ag⁺electrode), which was used in this example, with respect to the vacuumlevel is determined by calculation is specifically described. It isknown that the oxidation-reduction potential of ferrocene in methanol is+0.610 [V vs. SHE] with respect to the standard hydrogen electrode(Reference: Christian R. Goldsmith et al., J. Am. Chem. Soc., Vol. 124,No. 1, pp. 83-96, 2002). In contrast, using the reference electrode usedin this example, the oxidation-reduction potential of ferrocene inmethanol was calculated at +0.11 V [vs. Ag/Ag⁺]. Thus, it was found thatthe potential energy of this reference electrode was lower than that ofthe standard hydrogen electrode by 0.50 [eV].

Here, it is known that the potential energy of the standard hydrogenelectrode with respect to the vacuum level is −4.44 eV (Reference:Toshihiro Ohnishi and Tamami Koyama, High molecular EL material,Kyoritsu shuppan, pp. 64-67). Therefore, the potential energy of thereference electrode used in this example with respect to the vacuumlevel can be calculated as follows: −4.44−0.50=−4.94 [eV].

Example 2

In this example is described a light-emitting element using adibenzo[c,g]carbazole compound,7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA, structural formula (100)), as a host materialof a light-emitting layer using an emission center substance which emitsblue fluorescence and as a material of an electron-transport layer,which is a light-emitting element described in Embodiment 1.

The molecular structures of organic compounds used in this example areillustrated in structural formulae (i) to (iv) and (100) below. Theelement structure was similar to that illustrated in FIG. 1A.

Fabrication of Light-Emitting Element 1

First, a glass substrate over which indium tin oxide containing silicon(ITSO) had been formed to a thickness of 110 nm was prepared as thefirst electrode 101. A surface of the ITSO was covered with a polyimidefilm so that an area of 2 mm×2 mm of the surface was exposed. Theelectrode area was 2 mm×2 mm. As pretreatment for forming thelight-emitting element over this substrate, UV ozone treatment wasperformed for 370 seconds after washing of a surface of the substratewith water and baking that was performed at 200° C. for 1 hour. Afterthat, the substrate was transferred into a vacuum evaporation apparatuswhere the pressure had been reduced to approximately 10⁻⁴ Pa, and wassubjected to vacuum baking at 170° C. for 30 minutes in a heatingchamber of the vacuum evaporation apparatus, and then the substrate wascooled down for about 30 minutes.

Next, the substrate was fixed to a holder provided in the vacuumevaporation apparatus so that the surface of the substrate over whichthe ITSO film was formed faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, 9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: PCzPA) represented by the above structural formula (i)and molybdenum(VI)oxide were co-evaporated so that the ratio of PCzPA tomolybdenum oxide was 2:1 (weight ratio), thereby forming thehole-injection layer 111. The thickness of the hole-injection layer 111was set to 70 nm. Note that co-evaporation is an evaporation method inwhich a plurality of different substances is concurrently vaporized fromthe respective different evaporation sources.

Next, PCzPA was evaporated to a thickness of 30 nm, so that thehole-transport layer 112 was formed.

Further, over the hole-transport layer 112,7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA) represented by the above structural formula(100) andN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn) represented by the above structuralformula (iii) were co-evaporated to a thickness of 25 nm so that theratio of cgDBCzPA to 1,6mMemFLPAPrn was 1:0.03 (weight ratio), therebyforming the light-emitting layer 113.

Next, cgDBCzPA was evaporated to a thickness of 10 nm, and thenbathophenanthroline (abbreviation: BPhen) represented by the abovestructural formula (iv) was evaporated to a thickness of 15 nm, therebyforming the electron-transport layer 114.

Further, lithium fluoride was evaporated to a thickness of 1 nm over theelectron-transport layer 114, thereby forming the electron-injectionlayer. Lastly, aluminum was formed to a thickness of 200 nm as thesecond electrode 102 which serves as a cathode. Thus, the light-emittingelement 1 was completed. Note that in all the above evaporation steps,evaporation was performed by a resistance-heating method.

Fabrication of Comparison Light-Emitting Element 1

The comparison light-emitting element 1 was formed like thelight-emitting element 1, except for the light-emitting layer 113 andthe electron-transport layer 114. As to the light-emitting layer 113,after the hole-transport layer 112 was formed,9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA)represented by the above structural formula (ii) andN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPm) represented by the above structuralformula (iii) were co-evaporated to a thickness of 25 nm so that theratio of CzPA to 1,6mMemFLPAPrn was 1:0.05 (weight ratio), therebyforming the light-emitting layer 113.

After the light-emitting layer 113 was formed, CzPA was evaporated to athickness of 10 nm, and then bathophenanthroline (abbreviation: BPhen)represented by the above structural formula (iv) was evaporated to athickness of 15 nm, thereby forming the electron-transport layer 114.

The structure other than the light-emitting layer 113 and theelectron-transport layer 114 is similar to that of the light-emittingelement 1, and repetition of the explanation of the structure isavoided. Refer to the fabrication method of the light-emitting element1.

Thus, the comparison light-emitting element 1 was completed.

Operation Characteristics of Light-Emitting Element 1 and ComparisonLight-Emitting Element 1

The light-emitting element 1 and the comparison light-emitting element 1obtained as described above were sealed in a glove box containing anitrogen atmosphere so as not to be exposed to the air (specifically, asealing material was applied onto an outer edge of each element and heattreatment was performed at 80° C. for 1 hour at the time of sealing).Then, the operating characteristics of the light-emitting elements weremeasured. Note that the measurements were carried out at roomtemperature (in an atmosphere in which the temperature was kept at 25°C.).

FIG. 14 shows luminance versus current efficiency characteristics of thelight-emitting element 1 and the comparison light-emitting element 1,FIG. 15 shows voltage versus current characteristics, FIG. 16 showsluminance versus power efficiency characteristics, and FIG. 17 showsluminance versus external quantum efficiency characteristics. In FIG.14, the vertical axis represents current efficiency (cd/A) and thehorizontal axis represents luminance (cd/m²). In FIG. 15, the verticalaxis represents current (mA) and the horizontal axis represents voltage(V). In FIG. 16, the vertical axis represents power efficiency (lm/W)and the horizontal axis represents luminance (cd/m²). In FIG. 17, thevertical axis represents external quantum efficiency (%) and thehorizontal axis represents luminance (cd/m²).

As can be seen from FIG. 14, the luminance versus current efficiencycharacteristics of the light-emitting element 1 that provides bluefluorescence and uses cgDBCzPA, which is a dibenzo[c,g]carbazolecompound represented by the general formula (G1), as a host material ofa light-emitting layer and as an electron-transport material of anelectron-transport layer are favorable or substantially equal to theluminance versus current efficiency characteristics of the comparisonlight-emitting element 1 using CzPA like cgDBCzPA in the light-emittingelement 1. This indicates that the light-emitting element 1 is alight-emitting element having high emission efficiency.

As can be seen from FIG. 15, the voltage versus current characteristicsof the light-emitting element 1 are favorable or substantially equal tothose of the comparison light-emitting element 1, which indicates thatthe light-emitting element 1 is a light-emitting element having lowdriving voltage. This means that the dibenzo[c,g]carbazole compoundrepresented by the general formula (G1) has an excellentcarrier-transport property.

As can be seen from FIG. 16, the light-emitting element 1 exhibitsbetter luminance versus power efficiency characteristics than thelight-emitting element 1, which indicates that the light-emittingelement 1 is a light-emitting element having low power consumption.Thus, the light-emitting element 1 using cgDBCzPA, which is adibenzo[c,g]carbazole compound represented by the general formula (G1),is a light-emitting element having favorable characteristics such as lowdriving voltage and high emission efficiency.

As can be seen from FIG. 17, the luminance versus external quantumefficiency characteristics of the light-emitting element 1 are favorableand substantially equal to those of the comparison light-emittingelement 1, which indicates that the light-emitting element 1 is alight-emitting element having high emission efficiency.

FIG. 18 shows emission spectra obtained when a current of 0.1 mA wasmade to flow in the fabricated light-emitting element 1 and thecomparison light-emitting element 1. In FIG. 18, the vertical axisrepresents emission intensity (arbitrary unit) and the horizontal axisrepresents wavelength (nm). The emission intensity is shown as a valuerelative to the maximum emission intensity assumed to be 1. FIG. 18indicates that both the light-emitting element 1 and the comparisonlight-emitting element 1 emit blue light emission derived from1,6mMemFLPAPrn, which was the emission center substance.

Next, with an initial luminance set to 5000 cd/m², the light-emittingelement 1 and the comparison light-emitting element 1 were driven undera condition where the current density was constant, and changes inluminance relative to driving time were examined. FIG. 19 showsnormalized luminance versus time characteristics. FIG. 19 indicatesthat, although the comparison light-emitting element 1 using CzPA is alight-emitting element having a long lifetime, the light-emittingelement 1 using cgDBCzPA is an extremely reliable element having alonger lifetime than the comparison light-emitting element 1.

As compared with CzPA, cgDBCzPA is highly stable to evaporation and caneasily provide a light-emitting element having stable qualities.

As described above, cgDBCzPA is found to be a material with which alight-emitting element having the right combination of excellentcharacteristics can be provided.

Example 3

In this example is described a light-emitting element using adibenzo[c,g]carbazole compound,7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA, structural formula (100)), as a host materialof a light-emitting layer using an emission center substance which emitsblue fluorescence and as a material of an electron-transport layer,which is a light-emitting element described in Embodiment 1.

The molecular structures of organic compounds used in this example areillustrated in structural formulae (i) to (v) and (100) below. Theelement structure was similar to that illustrated in FIG. 1A.

Fabrication of Light-Emitting Element 2

First, a glass substrate over which indium tin oxide containing silicon(ITSO) had been formed to a thickness of 110 nm was prepared as thefirst electrode 101. A surface of the ITSO was covered with a polyimidefilm so that an area of 2 mm×2 mm of the surface was exposed. Theelectrode area was 2 mm×2 mm. As pretreatment for forming thelight-emitting element over this substrate, UV ozone treatment wasperformed for 370 seconds after washing of a surface of the substratewith water and baking that was performed at 200° C. for 1 hour. Afterthat, the substrate was transferred into a vacuum evaporation apparatuswhere the pressure had been reduced to approximately 10⁻⁴ Pa, and wassubjected to vacuum baking at 170° C. for 30 minutes in a heatingchamber of the vacuum evaporation apparatus, and then the substrate wascooled down for about 30 minutes.

Next, the substrate was fixed to a holder provided in the vacuumevaporation apparatus so that the surface of the substrate over whichthe ITSO film was formed faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, 9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: PCzPA) represented by the above structural formula (i)and molybdenum(VI)oxide were co-evaporated so that the ratio of PCzPA tomolybdenum oxide was 2:1 (weight ratio), thereby forming thehole-injection layer 111. The thickness of the hole-injection layer 111was set to 70 nm. Note that co-evaporation is an evaporation method inwhich a plurality of different substances is concurrently vaporized fromthe respective different evaporation sources.

Next, 3-[4-(9-phenanthryl)-phenyl]-9-phenyl-9H-carbazole (abbreviation:PCPPn) represented by the above structural formula (v) was evaporated toa thickness of 30 nm, so that the hole-transport layer 112 was formed.

Further, over the hole-transport layer 112,7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA) represented by the above structural formula(100) andN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn) represented by the above structuralformula (iii) were co-evaporated to a thickness of 25 nm so that theratio of cgDBCzPA to 1,6mMemFLPAPrn was 1:0.03 (weight ratio), therebyforming the light-emitting layer 113.

Next, cgDBCzPA was evaporated to a thickness of 10 nm, and thenbathophenanthroline (abbreviation: BPhen) represented by the abovestructural formula (iv) was evaporated to a thickness of 15 nm, therebyforming the electron-transport layer 114.

Further, lithium fluoride was evaporated to a thickness of 1 nm over theelectron-transport layer 114, thereby forming the electron-injectionlayer. Lastly, aluminum was formed to a thickness of 200 nm as thesecond electrode 102 which serves as a cathode. Thus, the light-emittingelement 2 was completed. Note that in all the above evaporation steps,evaporation was performed by a resistance-heating method.

Fabrication of Comparison Light-Emitting Element 2

The comparison light-emitting element 2 was formed like thelight-emitting element 2, except for the light-emitting layer 113 andthe electron-transport layer 114. As to the light-emitting layer 113,after the hole-transport layer 112 was formed,9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA)represented by the above structural formula (ii) andN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn) represented by the above structuralformula (iii) were co-evaporated to a thickness of 25 nm so that theratio of CzPA to 1,6mMemFLPAPrn was 1:0.05 (weight ratio), therebyforming the light-emitting layer 113.

After the light-emitting layer 113 was formed, CzPA was evaporated to athickness of 10 nm, and then bathophenanthroline (abbreviation: BPhen)represented by the above structural formula (iv) was evaporated to athickness of 15 nm, thereby forming the electron-transport layer 114.

The structure other than the light-emitting layer 113 and theelectron-transport layer 114 is similar to that of the light-emittingelement 2, and repetition of the explanation of the structure isavoided. Refer to the fabrication method of the light-emitting element2.

Thus, the comparison light-emitting element 2 was completed.

Operation Characteristics of Light-Emitting Element 2 and ComparisonLight-Emitting Element 2

The light-emitting element 2 and the comparison light-emitting element 2obtained as described above were sealed in a glove box containing anitrogen atmosphere so as not to be exposed to the air (specifically, asealing material was applied onto an outer edge of each element and heattreatment was performed at 80° C. for 1 hour at the time of sealing).Then, the operating characteristics of the light-emitting elements weremeasured. Note that the measurements were carried out at roomtemperature (in an atmosphere in which the temperature was kept at 25°C.).

FIG. 20 shows luminance versus current efficiency characteristics of thelight-emitting element 2 and the comparison light-emitting element 2,FIG. 21 shows voltage versus current characteristics, FIG. 22 showsluminance versus power efficiency characteristics, and FIG. 23 showsluminance versus external quantum efficiency characteristics. In FIG.20, the vertical axis represents current efficiency (cd/A) and thehorizontal axis represents luminance (cd/m²). In FIG. 21, the verticalaxis represents current (mA) and the horizontal axis represents voltage(V). In FIG. 22, the vertical axis represents power efficiency (lm/W)and the horizontal axis represents luminance (cd/m²). In FIG. 23, thevertical axis represents external quantum efficiency (%) and thehorizontal axis represents luminance (cd/m²).

As can be seen from FIG. 20, the luminance versus current efficiencycharacteristics of the light-emitting element 2 that provides bluefluorescence and uses cgDBCzPA, which is a dibenzo[c,g]carbazolecompound represented by the general formula (G1), as a host material ofa light-emitting layer and as an electron-transport material of anelectron-transport layer are substantially equal to the luminance versuscurrent efficiency characteristics of the comparison light-emittingelement 2 using CzPA like cgDBCzPA in the light-emitting element 2. Thisindicates that the light-emitting element 2 is a light-emitting elementhaving high emission efficiency.

As can be seen from FIG. 21, the light-emitting element 2 exhibitsbetter voltage versus current characteristics than the light-emittingelement 2, which indicates that the light-emitting element 2 is alight-emitting element having low driving voltage. This means that thedibenzo[c,g]carbazole compound represented by the general formula (G1)has an excellent carrier-transport property.

As can be seen from FIG. 22, the light-emitting element 2 exhibits veryfavorable luminance versus power efficiency characteristics better thanthose of the comparison light-emitting element 2, which indicates thatthe light-emitting element 2 is a light-emitting element having lowpower consumption. Thus, the light-emitting element 2 using cgDBCzPAwhich is a dibenzo[c,g]carbazole compound represented by the generalformula (G1) is a light-emitting element having favorablecharacteristics such as low driving voltage and high emissionefficiency.

As can be seen from FIG. 23, the luminance versus external quantumefficiency characteristics of the light-emitting element 2 are favorableand substantially equal to those of the comparison light-emittingelement 2, which indicates that the light-emitting element 2 is alight-emitting element having very high emission efficiency.

FIG. 24 shows emission spectra obtained when a current of 0.1 mA wasmade to flow in the fabricated light-emitting element 2 and thecomparison light-emitting element 2. In FIG. 24, the vertical axisrepresents emission intensity (arbitrary unit) and the horizontal axisrepresents wavelength (nm). The emission intensity is shown as a valuerelative to the maximum emission intensity assumed to be 1. FIG. 24shows the spectra of the light-emitting element 2 and the comparisonlight-emitting element 2 overlaps completely, which indicates that bothelements emit blue light emission derived from 1,6mMemFLPAPrn, which wasthe emission center substance.

Next, with an initial luminance set to 5000 cd/m², the light-emittingelement 2 and the comparison light-emitting element 2 were driven undera condition where the current density was constant, and changes inluminance relative to driving time were examined. FIG. 25 showsnormalized luminance versus time characteristics. FIG. 25 indicatesthat, although the comparison light-emitting element 2 using CzPA is alight-emitting element having a long lifetime, the light-emittingelement 2 using cgDBCzPA is an extremely reliable element having alonger lifetime than the comparison light-emitting element 2.

As compared with CzPA, cgDBCzPA is highly stable to evaporation and caneasily provide a light-emitting element having stable qualities.

As described above, it is also confirmed in this example that cgDBCzPAis found to be a material with which a light-emitting element having theright combination of excellent characteristics can be provided.

Example 4

In this example is described a light-emitting element using adibenzo[c,g]carbazole compound,7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA, structural formula (100)), as a host materialof a light-emitting layer using an emission center substance which emitsblue fluorescence and as a material of an electron-transport layer,which is a light-emitting element described in Embodiment 1.

The molecular structures of organic compounds used in this example areillustrated in structural formulae (i) to (vi) and (100) below. Theelement structure was similar to that illustrated in FIG. 1A.

Fabrication of Light-Emitting Element 3

First, a glass substrate over which indium tin oxide containing silicon(ITSO) had been formed to a thickness of 110 nm was prepared as thefirst electrode 101. A surface of the ITSO was covered with a polyimidefilm so that an area of 2 mm×2 mm of the surface was exposed. Theelectrode area was 2 min×2 mm. As pretreatment for forming thelight-emitting element over this substrate, UV ozone treatment wasperformed for 370 seconds after washing of a surface of the substratewith water and baking that was performed at 200° C. for 1 hour. Afterthat, the substrate was transferred into a vacuum evaporation apparatuswhere the pressure had been reduced to approximately 10⁻⁴ Pa, and wassubjected to vacuum baking at 170° C. for 30 minutes in a heatingchamber of the vacuum evaporation apparatus, and then the substrate wascooled down for about 30 minutes.

Next, the substrate was fixed to a holder provided in the vacuumevaporation apparatus so that the surface of the substrate over whichthe ITSO film was formed faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, 9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: PCzPA) represented by the above structural formula (i)and molybdenum(VI)oxide were co-evaporated so that the ratio of PCzPA tomolybdenum oxide was 2:1 (weight ratio), thereby forming thehole-injection layer 111. The thickness of the hole-injection layer 111was set to 50 nm. Note that co-evaporation is an evaporation method inwhich a plurality of different substances is concurrently vaporized fromthe respective different evaporation sources.

Next, PCzPA was evaporated to a thickness of 10 nm, so that thehole-transport layer 112 was formed.

Further, over the hole-transport layer 112,7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA) represented by the above structural formula(100) andN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn) represented by the above structuralformula (iii) were co-evaporated to a thickness of 30 nm so that theratio of cgDBCzPA to 1,6mMemFLPAPrn was 1:0.05 (weight ratio), therebyforming the light-emitting layer 113.

Next, tris(8-quinolinolato)aluminum(III) (abbreviation: Alq) representedby the above structural formula (vi) was evaporated to a thickness of 10nm, and then bathophenanthroline (abbreviation: BPhen) represented bythe above structural formula (iv) was evaporated to a thickness of 15nm; thereby forming the electron-transport layer 114.

Further, lithium fluoride was evaporated to a thickness of 1 nm over theelectron-transport layer 114, thereby forming the electron-injectionlayer. Lastly, aluminum was formed to a thickness of 200 nm as thesecond electrode 102 which serves as a cathode. Thus, the light-emittingelement 3 was completed. Note that in all the above evaporation steps,evaporation was performed by a resistance-heating method.

Fabrication of Comparison Light-Emitting Element 3

The comparison light-emitting element 3 was formed like thelight-emitting element 3, except for the light-emitting layer 113. Forthe comparison light-emitting element 3, after the hole-transport layer112 was formed, 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: CzPA) represented by the above structural formula (ii)andN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn) represented by the above structuralformula (iii) were co-evaporated to a thickness of 30 nm so that theratio of CzPA to 1,6mMemFLPAPrn was 1:0.05 (weight ratio), therebyforming the light-emitting layer 113.

The structure other than the light-emitting layer 113 is similar to thatof the light-emitting element 3, and repetition of the explanation ofthe structure is avoided. Refer to the fabrication method of thelight-emitting element 3.

Thus, the comparison light-emitting element 3 was completed.

Operation Characteristics of Light-Emitting Element 3 and ComparisonLight-Emitting Element 3

The light-emitting element 3 and the comparison light-emitting element 3obtained as described above were sealed in a glove box containing anitrogen atmosphere so as not to be exposed to the air (specifically, asealing material was applied onto an outer edge of each element and heattreatment was performed at 80° C. for 1 hour at the time of sealing).Then, the operating characteristics of the light-emitting elements weremeasured. Note that the measurements were carried out at roomtemperature (in an atmosphere in which the temperature was kept at 25°C.).

FIG. 26 shows luminance versus current efficiency characteristics of thelight-emitting, element 3 and the comparison light-emitting element 3,and FIG. 27 shows voltage versus current characteristics. In FIG. 26,the vertical axis represents current efficiency (cd/A) and thehorizontal axis represents luminance (cd/m²). In FIG. 27, the verticalaxis represents current (mA) and the horizontal axis represents voltage(V).

As can be seen from FIG. 26, the luminance versus current efficiencycharacteristics of the light-emitting element 3 that provides bluefluorescence and uses cgDBCzPA, which is a dibenzo[c,g]carbazolecompound represented by the general formula (G1), as a host material ofa light-emitting layer and as an electron-transport material of anelectron-transport layer are equal to the luminance versus currentefficiency characteristics of the comparison light-emitting element 3using CzPA like cgDBCzPA in the light-emitting element 3. This indicatesthat the light-emitting element 3 is a light-emitting element havinghigh emission efficiency.

As can be seen from FIG. 27, the light-emitting element 3 has muchbetter voltage versus current characteristics than the comparisonlight-emitting element 3, which indicates that the light-emittingelement 3 is a light-emitting element having low driving voltage. Thismeans that the dibenzo[c,g]carbazole compound represented by the generalformula (G1) has an excellent carrier-transport property.

FIG. 28 shows emission spectra obtained when a current of 0.1 mA wasmade to flow in the fabricated light-emitting element 3 and thecomparison light-emitting element 3. In FIG. 28, the vertical axisrepresents emission intensity (arbitrary unit) and the horizontal axisrepresents wavelength (nm). The emission intensity is shown as a valuerelative to the maximum emission intensity assumed to be 1. FIG. 28shows the spectra of the light-emitting element 3 and the comparisonlight-emitting element 3 are not greatly different, which indicates thatboth elements emit blue light emission derived from 1,6mMemFLPAPrn,which was the emission center substance.

As compared with CzPA, cgDBCzPA is highly stable to evaporation and caneasily provide a light-emitting element having stable qualities.

As described above, it is also confirmed in this example that cgDBCzPAis found to be a material with which a light-emitting element having theright combination of excellent characteristics can be provided.

Example 5

In this example is described a light-emitting element using adibenzo[c,g]carbazole compound,7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA, structural formula (100)), as a host materialof a light-emitting layer using an emission center substance which emitsblue fluorescence and as a material of an electron-transport layer,which is a light-emitting element described in Embodiment 1.

The molecular structures of organic compounds used in this example areillustrated in structural formulae (i), (iii), (iv), (vi) to (viii), and(100) below. The element structure was similar to that illustrated inFIG. 1A.

Fabrication of Light-Emitting Element 4

First, a glass substrate over which indium tin oxide containing silicon(ITSO) had been formed to a thickness of 110 nm was prepared as thefirst electrode 101. A surface of the ITSO was covered with a polyimidefilm so that an area of 2 mm×2 mm of the surface was exposed. Theelectrode area was 2 mm×2 mm. As pretreatment for forming thelight-emitting element over this substrate, UV ozone treatment wasperformed for 370 seconds after washing of a surface of the substratewith water and baking that was performed at 200° C. for 1 hour. Afterthat, the substrate was transferred into a vacuum evaporation apparatuswhere the pressure had been reduced to approximately 10⁻⁴ Pa, and wassubjected to vacuum baking at 170° C. for 30 minutes in a heatingchamber of the vacuum evaporation apparatus, and then the substrate wascooled down for about 30 minutes.

Next, the substrate was fixed to a holder provided in the vacuumevaporation apparatus so that the surface of the substrate over whichthe ITSO film was formed faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, 9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: PCzPA) represented by the above structural formula (i)and molybdenum(VI)oxide were co-evaporated so that the ratio of PCzPA tomolybdenum oxide was 2:1 (weight ratio), thereby forming thehole-injection layer 111. The thickness of the hole-injection layer 111was set to 50 nm. Note that co-evaporation is an evaporation method inwhich a plurality of different substances is concurrently vaporized fromthe respective different evaporation sources.

Next, PCzPA was evaporated to a thickness of 10 nm, so that thehole-transport layer 112 was formed.

Further, over the hole-transport layer 112,7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA) represented by the above structural formula(100) andN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn) represented by the above structuralformula (iii) were co-evaporated to a thickness of 25 nm so that theratio of cgDBCzPA to 1,6mMemFLPAPrn was 1:0.03 (weight ratio), therebyforming the light-emitting layer 113.

Next, tris(8-quinolinolato)aluminum(III) (abbreviation: Alq) representedby the above structural formula (vi) was evaporated to a thickness of 10nm, and then bathophenanthroline (abbreviation: BPhen) represented bythe above structural formula (iv) was evaporated to a thickness of 15nm, thereby forming the electron-transport layer 114.

Further, lithium fluoride was evaporated to a thickness of 1 nm over theelectron-transport layer 114, thereby forming the electron-injectionlayer. Lastly, aluminum was formed to a thickness of 200 nm as thesecond electrode 102 which serves as a cathode. Thus, the light-emittingelement 4 was completed. Note that in all the above evaporation steps,evaporation was performed by a resistance-heating method.

Fabrication of Comparison Light-Emitting Element 4-1

The comparison light-emitting element 4-1 was formed like thelight-emitting element 4, except for the light-emitting layer 113. Forthe comparison light-emitting element 4-1, after the hole-transportlayer 112 was formed, a known anthracene derivative represented by theabove structural formula (vii) andN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn) represented by the above structuralformula (iii) were co-evaporated to a thickness of 25 nm so that theratio of the anthracene derivative to 1,6mMemFLPAPrn was 1:0.03 (weightratio), thereby forming the light-emitting layer 113.

The structure other than the light-emitting layer 113 is similar to thatof the light-emitting element 4, and repetition of the explanation ofthe structure is avoided. Refer to the fabrication method of thelight-emitting element 4.

Thus, the comparison light-emitting element 4-1 was completed.

Fabrication of Comparison Light-Emitting Element 4-2

The comparison light-emitting element 4-2 was formed like thelight-emitting element 4, except for the light-emitting layer 113. Forthe comparison light-emitting element 4-2, after the hole-transportlayer 112 was formed, a known anthracene derivative represented by theabove structural formula (viii) andN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn) represented by the above structuralformula (iii) were co-evaporated to a thickness of 25 nm so that theratio of the anthracene derivative to 1,6mMemFLPAPrn was 1:0.03 (weightratio), thereby forming the light-emitting layer 113.

The structure other than the light-emitting layer 113 is similar to thatof the light-emitting element 4, and repetition of the explanation ofthe structure is avoided. Refer to the fabrication method of thelight-emitting element 4.

Thus, the comparison light-emitting element 4-2 was completed.

Operation Characteristics of Light-Emitting Element 4 and ComparisonLight-Emitting Elements 4-1 and 4-2

The light-emitting element 4 and the comparison light-emitting elements4-1 and 4-2 obtained as described above were sealed in a glove boxcontaining a nitrogen atmosphere so as not to be exposed to the air(specifically, a sealing material was applied onto an outer edge of eachelement and heat treatment was performed at 80° C. for 1 hour at thetime of sealing). Then, the operating characteristics of thelight-emitting elements were measured. Note that the measurements werecarried out at room temperature (in an atmosphere in which thetemperature was kept at 25° C.).

FIG. 29 shows current density versus luminance characteristics of thelight-emitting element 4 and the comparison light-emitting elements 4-1and 4-2, FIG. 30 shows luminance versus current efficiencycharacteristics, FIG. 31 shows voltage versus current characteristics,FIG. 32 shows luminance versus power efficiency characteristics, andFIG. 33 shows voltage versus luminance characteristics. In FIG. 29, thevertical axis represents luminance (cd/m²) and the horizontal axisrepresents current density (mA/cm²). In FIG. 30, the vertical axisrepresents current efficiency (cd/A) and the horizontal axis representsluminance (cd/m²). In FIG. 31, the vertical axis represents current (mA)and the horizontal axis represents voltage (V). In FIG. 32, the verticalaxis represents power efficiency (lm/W) and the horizontal axisrepresents luminance (cd/m²). In FIG. 33, the vertical axis representsluminance (cd/m²) and the horizontal axis represents voltage (V).

As can be seen from FIG. 29, the light-emitting element 4 and thecomparison light-emitting elements 4-1 and 4-2 have substantially equalcurrent density versus luminance characteristics. In addition, FIG. 30reveals that the light-emitting element 4 and the comparisonlight-emitting elements 4-1 and 4-2 have substantially equal luminanceversus current efficiency characteristics, at a luminance of at least1000 cd/m² or more which is a practical luminance.

Furthermore, FIG. 31 reveals that the light-emitting element 4 exhibitsmuch better voltage versus current characteristics than the comparisonlight-emitting elements 4-1 and 4-2. This indicates the favorablecarrier-transport property of cgDBCzPA. Thus, also as seen from FIG. 32,the light-emitting element 4 is found to be an element having highlyfavorable luminance versus power efficiency characteristics. Note thatFIG. 33 shows high driving voltage of the comparison light-emittingelements 4-1 and 4-2, and in order to achieve a luminance of 1000 cd/m²,which is of practical use, a voltage of about 3.3 V needs to be appliedto the light-emitting element 4 but a voltage of 4 V or more needs to beapplied to each of the comparison light-emitting elements 4-1 and 4-2.The driving voltage of the comparison light-emitting element 4-1 isespecially high.

FIG. 34 shows emission spectra obtained when a current of 0.1 mA wasmade to flow in the fabricated light-emitting element 4 and thecomparison light-emitting element 4-1 and 4-2. In FIG. 34, the verticalaxis represents emission intensity (arbitrary unit) and the horizontalaxis represents wavelength (nm). The emission intensity is shown as avalue relative to the maximum emission intensity assumed to be 1. FIG.34 shows the spectra of the light-emitting element 4 and the comparisonlight-emitting element 4-1 and 4-2 are not greatly different, whichindicates that both elements emit blue light emission derived from1,6mMemFLPAPrn, which was the emission center substance.

Next, with an initial luminance set to 5000 cd/m², the light-emittingelement 4 and the comparison light-emitting elements 4-1 and 4-2 weredriven under a condition where the current density was constant, andchanges in luminance relative to driving time were examined. FIG. 35shows normalized luminance versus time characteristics. FIG. 35 showsthat the comparison light-emitting element 4-2 using the substancerepresented by the above structural formula (viii) has a shorterlifetime than the other elements. In addition, although the comparisonlight-emitting element 4-1 using the substance represented by the abovestructural formula (vii) instead of cgDBCzPA has a lifetime equal tothat of the light-emitting element 4 at a glance, the comparisonlight-emitting element 4-1 exhibits not only a rise in initial luminancebut also an increase in deterioration rate after a certain time point;consequently, the half life of the comparison light-emitting element 4-1is estimated at about half of that of the light-emitting element 4.

Thus, the comparison light-emitting element 4-1 has a drawback indriving voltage and the comparison light-emitting element 4-2 hasdrawbacks in both driving voltage and lifetime, and it is difficult foreach element to have the right combination of characteristics. Incontrast, by using cgDBCzPA, a high-performance light-emitting elementwhich has excellent combination of characteristics in terms ofefficiency, driving voltage, and lifetime is found to be able to befabricated. What is remarkable is the driving voltage, which enables alight-emitting element having very high power efficiency to be provided.

As described above, it is also confirmed in this example that cgDBCzPAis found to be a material with which a light-emitting element having theright combination of excellent characteristics can be provided.

Example 6

In this example is described a synthesis method of7-[4-(10-phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(abbreviation: cgDBCzPA), which is a dibenzo[c,g]carbazole compoundrepresented by the general formula (G1) described in Embodiment 2, whichis different from the synthesis method in Example 1.

The steps up to and including synthesis of 7H-dibenzo[c,g]carbazole werethe same as Steps 1 and 2 in Example 1.

Step 3: 7-(4-Bromophenyl)-7H-dibenzo[c,g]carbazole

In a 200 mL three-neck flask were placed 5.0 g (18 mmol) of7H-dibenzo[c,g]carbazole, 13 g (47 mol) of 4-bromoiodobenzene, and 1.9 g(20 mmol) of sodium tert-butoxide. After the air in the flask wasreplaced with nitrogen, to this mixture were added 100 mL of mesityleneand 0.90 mL of tri-(tert-butyl)phosphine (a 10 wt % hexane solution).This mixture was degassed by being stirred while the pressure wasreduced. After the degassing, 0.51 g (0.90 mmol) ofbis(dibenzylideneacetone)palladium(0) was added to this mixture. Thismixture was stirred at 170° C. for 17 hours under a nitrogen stream.After the stirring, 20 mL of water was added to the obtained mixture.The aqueous layer of this mixture was extracted with toluene, and thesolution of the extract and the organic layer were combined and washedwith saturated brine. The organic layer was dried with magnesiumsulfate, and this mixture was gravity-filtered. A solid obtained byconcentration of the obtained filtrate was dissolved in about 30 mL oftoluene. This solution was suction-filtered through Celite (manufacturedby Wako Pure Chemical Industries, Ltd., Catalog No. 531-16855), alumina,and Florisil (manufactured by Wako Pure Chemical Industries, Ltd.,Catalog No. 540-00135). A solid obtained by concentration of thefiltrate was recrystallized from toluene/hexane to give 2.9 g of paleyellow needle-like crystals, which was the object of the synthesis, in ayield of 38% yield. A reaction scheme (c-2) of Step 3 is illustratedbelow.

Step 4: 7-[4-(10-Phenyl-9-anthryl)phenyl]-7H-dibenzo[c,g]carbazole(cgDBCzPA)

In a 200 mL three-neck flask were placed 1.7 g (4.0 mmol) of7-(4-bromophenyl)-7H-dibenzo[c,g]carbazole and 1.2 g (4.0 mmol) of10-phenylanthracene-9-boronic acid, and the air in the flask wasreplaced with nitrogen. To this mixture were added 15 mL of toluene, 5.0mL of ethanol, and 4.0 mL of an aqueous solution of sodium carbonate.This mixture was degassed by being stirred while the pressure wasreduced. To this mixture was added 0.23 g (0.20 mmol) oftetrakis(triphenylphosphine)palladium(0), and the mixture was stirred at90° C. for 10 hours under a nitrogen stream, so that a solid wasprecipitated. The precipitated solid was removed by suction filtration.The collected solid was dissolved in about 50 mL of hot toluene, andthis solution was suction-filtered through Celite (produced by Wako PureChemical Industries, Ltd., Catalog No. 531-16855), alumina, and Florisil(produced by Wako Pure Chemical Industries, Ltd., Catalog No.540-00135). A solid obtained by concentration of the filtrate was washedwith toluene/hexane to give 1.3 g of a pale yellow powder, which was theobject of the synthesis, in a yield of 55%. A synthesis scheme (d-2) ofStep 4 is illustrated below.

By a train sublimation method, 1.3 g of the obtained pale yellow powderysolid was purified by sublimation. In the sublimation purification,cgDBCzPA was heated at 300° C. under a pressure of 3.6 Pa with a flowrate of argon at 5.0 mL/min. After the sublimation purification, 1.1 gof a pale yellow solid of cgDBCzPA was recovered in 86% yield.

Reference Example 1

A method of synthesizingN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn) used in the above examples is described.

Step 1: Synthesis of3-Methylphenyl-3-(9-phenyl-9H-fluoren-9-yl)phenylamine (abbreviation:mMemFLPA)

There were placed 3.2 g (8.1 mmol) of 9-(3-bromophenyl)-9-phenylfluoreneand 2.3 g (24.1 mmol) of sodium tert-butoxide in a 200 mL three-neckflask. The air in the flask was replaced with nitrogen. Then, 40.0 mL oftoluene, 0.9 mL (8.3 mmol) of m-toluidine, and 0.2 mL of a 10% hexanesolution of tri(tert-butyl)phosphine were added to this mixture. Thetemperature of this mixture was set to 60° C., and 44.5 mg (0.1 mmol) ofbis(dibenzylideneacetone)palladium(0) was added to the mixture. Thetemperature of the mixture was raised to 80° C., and the mixture wasstirred for 2.0 hours. After the stirring, the mixture wassuction-filtered through Florisil (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 540-00135), Celite (produced by Wako PureChemical Industries, Ltd., Catalog No. 531-16855), and alumina to give afiltrate. The filtrate was concentrated to give a solid, which was thenpurified by silica gel column chromatography (developing solvent:hexane/toluene in a 1:1 ratio). Recrystallization from a mixed solventof toluene and hexane gave 2.8 g of a white solid, which was the objectof the synthesis, in 82% yield. A synthesis scheme of the above Step 1is illustrated below.

Step 2: Synthesis ofN,N′-Bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn)

There were placed 0.6 g (1.7 mmol) of 1,6-dibromopyrene, 1.4 g (3.4mmol) of 3-methylphenyl-3-(9-phenyl-9H-fluoren-9-yl)phenylamine obtainedin Step 1 above, and 0.5 g (5.1 mmol) of sodium tert-butoxide in a 100mL three-neck flask. The air in the flask was replaced with nitrogen. Tothis mixture were added 21.0 mL of toluene and 0.2 mL of a 10% hexanesolution of tri(tert-butyl)phosphine. The temperature of this mixturewas set to 60° C., and 34.9 mg (0.1 mmol) ofbis(dibenzylideneacetone)palladium(0) was added to the mixture. Thetemperature of this mixture was set to 80° C., and the mixture wasstirred for 3.0 hours. After the stirring, 400 mL of toluene was addedto the mixture, and the mixture was heated. While the mixture it wassuction-filtered through Florisil (produced by Wako Pure ChemicalIndustries, was kept hot, Ltd., Catalog No. 540-00135), Celite (producedby Wako Pure Chemical Industries, Ltd., Catalog No. 531-16855), andalumina to give a filtrate. The filtrate was concentrated to give asolid, which was then purified by silica gel column chromatography(developing solvent: hexane/toluene in a 3:2 ratio) to give a yellowsolid. Recrystallization of the obtained yellow solid from a mixedsolvent of toluene and hexane gave 1.2 g of a yellow solid, which wasthe object of the synthesis, in 67% yield.

By a train sublimation method, 1.0 g of the obtained yellow solid waspurified. In the purification, the yellow solid was heated at 317° C.under a pressure of 2.2 Pa with a flow rate of argon gas of 5.0 mL/min.After the purification, 1.0 g of a yellow solid, which was the object ofthe synthesis, in 93% yield. A synthesis scheme of the above Step 2 isillustrated below.

A nuclear magnetic resonance (NMR) spectroscopy identified this compoundasN,N′-bis(3-methylphenyl)-N,N′-bis[3-(9-phenyl-9H-fluoren-9-yl)phenyl]-pyrene-1,6-diamine(abbreviation: 1,6mMemFLPAPrn), which was the object of the synthesis.

¹H NMR data of the obtained compound are shown below.

¹H NMR (CDCl₃, 300 MHz): δ=2.21 (s, 6H), 6.67 (d, J=7.2 Hz, 2H), 6.74(d, J=7.2 Hz, 2H), 7.17-7.23 (m, 34H), 7.62 (d, J=7.8 Hz, 4H), 7.74 (d,J=7.8 Hz, 2H), 7.86 (d, J=9.0 Hz, 2H), 8.04 (d, J=8.7 Hz, 4H).

Reference Example 2

An example of synthesis of3-[4-(9-phenanthryl)-phenyl]-9-phenyl-9H-carbazole (abbreviation: PCPPn)is described.

Step 1: Synthesis of 4-(9-Phenyl-9H-carbazol-3-yl)phenylboronic acid

In a 300 mL three-neck flask, 8.0 g (20 mmol) of3-(4-bromophenyl)-9-phenyl-9H-carbazole was placed, the air in the flaskwas replaced with nitrogen, 100 mL of dehydrated tetrahydrofuran(abbreviation: THF) was added, and the temperature was lowered to −78°C. Into this mixture solution, 15 mL (24 mmol) of a 1.65 mol/Ln-butyllithium hexane solution was dropped, and the mixture solutionwith the n-butyllithium hexane solution added was stirred for 2 hours.To this mixture, 3.4 mL (30 mmol) of trimethyl borate was added, and themixture was stirred at −78° C. for 2 hours and at room temperature for18 hours. After the reaction, a 1M diluted hydrochloric acid was addedto this reaction solution until the solution became acid, and thesolution with the diluted hydrochloric acid added was stirred for 7hours. This solution was subjected to extraction with ethyl acetate, andthe obtained organic layer was washed with a saturated aqueous sodiumchloride solution. After the washing, magnesium sulfate was added to theorganic layer to adsorb moisture. This suspension was filtered, and theobtained filtrate was concentrated, and hexane was added thereto. Themixture was irradiated with supersonic waves and then recrystallized togive 6.4 g of a white powder, which was the object of synthesis, in ayield of 88%. A reaction scheme of Step 1 described above is illustratedbelow.

The Rf values of the substance that was the object of synthesis and3-(4-bromophenyl)-9-phenyl-9H-carbazole were respectively 0 (origin) and0.53, which were found by silica gel thin layer chromatography (TLC)(developing solvent: ethyl acetate/hexane in a 1:10 ratio). In addition,the Rf values of the object of the synthesis and3-(4-bromophenyl)-9-phenyl-9H-carbazole were respectively 0.72 and 0.93,which were found by silica gel thin layer chromatography (TLC) usingethyl acetate as a developing solvent.

Step 2: Synthesis of 3-[4-(9-Phenanthryl)-phenyl]-9-phenyl-9H-carbazole(abbreviation: PCPPn)

In a 200 mL three-neck flask, a mixture of 1.5 g (5.0 mmol) of9-phenyl-9H-carbazol-3-yl-phenyl-4-boronic acid, 3.2 g (11 mmol) of9-bromophenanthrene, 11 mg (0.1 mmol) of palladium(II)acetate, 30 mg(0.1 mmol) of tri(ortho-tolyl)phosphine, 30 mL of toluene, 3 mL ofethanol, and 5 mL of a 2 mol/L aqueous solution of potassium carbonatewas degassed while being stirred under reduced pressure, and reacted bybeing stirred and heated at 90° C. for 6 hours under a nitrogenatmosphere.

After the reaction, 200 mL of toluene was added to this reaction mixturesolution, and the organic layer of the mixture solution was filteredthrough Florisil, alumina, and Celite. The obtained filtrate was washedwith water, and magnesium sulfate was added thereto so that moisture wasadsorbed. This suspension was filtered to obtain a filtrate. Theobtained filtrate was concentrated and purified by silica gel columnchromatography. At this time, a mixed solvent of toluene and hexane(toluene:hexane=1:4) was used as a developing solvent for thechromatography. The obtained fraction was concentrated, and acetone andmethanol were added thereto. The mixture was irradiated with ultrasonicwaves and then recrystallized, so that PCPPn, which was the object ofthe synthesis, was obtained as 2.2 g of a white powder in a yield of75%. A reaction scheme of Step 2 is illustrated below.

The Rf values of the substance that was the object of the synthesis and9-bromophenanthrene were respectively 0.33 and 0.70, which were found bysilica gel thin layer chromatography (TLC) (developing solvent: ethylacetate/hexane in a 1:10 ratio).

The obtained compound was subjected to nuclear magnetic resonance (NMR)spectroscopy. The measurement results confirmed that PCPPn was obtained.The measurement data are as follows:

¹H NMR (CDCl₃, 300 MHz): δ (ppm)=7.30-7.35 (m, 11H), 7.43-7.78 (m, 16H),7.86-7.93 (m, 3H), 8.01 (dd, J=0.9 Hz, 7.8 Hz, 1H), 8.23 (d, J=7.8 Hz,1H), 8.47 (d, J=1.5 Hz, 1H), 8.74 (d, J=8.1 Hz, 1H), 8.80 (d, J=7.8 Hz,1H).

REFERENCE NUMERALS

-   101: first electrode, 102: second electrode, 103: EL layer, 111:    hole-injection layer, 112: hole-transport layer, 113: light-emitting    layer, 114: electron-transport layer, 115: electron-injection layer,    400: substrate, 401: first electrode, 402: auxiliary electrode, 403:    EL layer, 404: second electrode, 405: sealing material, 406: sealing    material, 407: sealing substrate, 408: space, 412: pad, 420: IC    chip, 501: first electrode, 502: second electrode, 511: first    light-emitting unit, 512: second light-emitting unit, 513: charge    generation layer, 601: driver circuit portion (source line driver    circuit), 602: pixel portion, 603: driver circuit portion (gate line    driver circuit), 604: sealing substrate, 605: sealing material, 607:    space, 608: wiring, 609: FPC (flexible printed circuit), 610:    element substrate, 611: switching TFT, 612: current control TFT,    613: first electrode, 614: insulator, 616: EL layer, 617: second    electrode, 618: light-emitting element, 623: n-channel TFT, 624:    p-channel TFT, 901: housing, 902: liquid crystal layer, 903:    backlight unit, 904: housing, 905: driver IC, 906: terminal, 951:    substrate, 952: electrode, 953: insulating layer, 954: partition    layer, 955: EL layer, 956: electrode, 1201: source electrode, 1202:    active layer, 1203: drain electrode, 1204: gate electrode, 2001:    housing, 2002: light source, 3001: lighting device, 5000: display    region, 5001: display region, 5002: display region, 5003: display    region, 5004: display region, 5005: display region, 7101: housing,    7103: display portion, 7105: stand, 7107: display portion, 7109:    operation key, 7110: remote control, 7201: main body, 7202: housing,    7203: display portion, 7204: keyboard, 7205: external connection    port, 7206: pointing device, 7301: housing, 7302: housing, 7303:    joint portion, 7304: display portion, 7305: display portion, 7306:    speaker portion, 7307: recording medium insertion portion, 7308: LED    lamp, 7309: operation key, 7310: connection terminal, 7311: sensor,    7401: housing, 7402: display portion, 7403: operation button, 7404:    external connection port, 7405: speaker, 7406: microphone, 7400:    mobile phone.

This application is based on Japanese Patent Application Serial No.2011-161161 filed with the Japan Patent Office on Jul. 22, 2011, theentire contents of which are hereby incorporated by reference.

The invention claimed is:
 1. A compound comprising: adibenzo[c,g]carbazole skeleton; and an aryl group bonded to a 7-positionof the dibenzo[c,g]carbazole skeleton, wherein the aryl group has 14 to30 carbon atoms and includes at least an anthracene skeleton, andwherein the anthracene skeleton is bonded to the 7-position of thedibenzo[c,g]carbazole skeleton through a phenylene group.
 2. Thecompound according to claim 1, wherein the 7-position of thedibenzo[c,g]carbazole skeleton and a 9-position of the anthraceneskeleton are bonded through the phenylene group.
 3. The compoundaccording to claim 1, wherein the aryl group is a substituted orunsubstituted anthryl phenyl group, and wherein the substituted orunsubstituted anthryl phenyl group has 20 to 30 carbon atoms.
 4. Thecompound according to claim 1, wherein the aryl group is a substitutedor unsubstituted (9-anthryl)phenyl group, and wherein the substituted orunsubstituted (9-anthryl)phenyl group has 20 to 30 carbon atoms.
 5. Alight-emitting element comprising a dibenzo[c,g]carbazole compoundcomprising: a dibenzo[c,g]carbazole skeleton; and an aryl group bondedto a 7-position of the dibenzo[c,g]carbazole skeleton, wherein the arylgroup has 14 to 30 carbon atoms and includes at least an anthraceneskeleton, and wherein the anthracene skeleton is bonded to the7-position of the dibenzo[c,g]carbazole skeleton through a phenylenegroup.
 6. The light-emitting element according to claim 5, wherein the7-position of the dibenzo[c,g]carbazole skeleton and a 9-position of theanthracene skeleton are bonded through the phenylene group.
 7. Thelight-emitting element according to claim 5, wherein the aryl group is asubstituted or unsubstituted anthryl phenyl group, and wherein thesubstituted or unsubstituted anthryl phenyl group has 20 to 30 carbonatoms.
 8. The light-emitting element according to claim 5, wherein thearyl group is a substituted or unsubstituted (9-anthryl)phenyl group,and wherein the substituted or unsubstituted (9-anthryl)phenyl group has20 to 30 carbon atoms.
 9. A lighting device comprising thelight-emitting element according to claim
 5. 10. A display devicecomprising the light-emitting element according to claim
 5. 11. Acompound represented by a general formula (G2),

wherein α represents a substituted or unsubstituted phenylene group,wherein β represents a substituted or unsubstituted anthryl group, andwherein R¹¹ to R²² each independently represent any of hydrogen, analkyl group having 1 to 4 carbon atoms, and an aryl group having 6 to 12carbon atoms.
 12. The compound according to claim 11, wherein thecompound is represented by a general formula (G3),

wherein R⁵ represents any of hydrogen, an alkyl group having 1 to 4carbon atoms, and an aryl group having 6 to 10 carbon atoms, wherein R¹,R², R³, R⁴, R⁶, R⁷, R⁸, and R⁹ each independently represent hydrogen oran alkyl group having 1 to 4 carbon atoms, and wherein α represents asubstituted or unsubstituted phenylene group.
 13. The compound accordingto claim 11,

wherein a total number of carbon atoms of α and β is 20 to
 30. 14. Thecompound according to claim 11, wherein the compound is represented by ageneral formula (G5),

wherein R⁵ represents any of hydrogen, an alkyl group having 1 to 4carbon atoms, and an aryl group having 6 to 10 carbon atoms, wherein R¹,R², R³, R⁴, R⁶, R⁷, R⁸, and R⁹ each independently represent hydrogen oran alkyl group having 1 to 4 carbon atoms, wherein α represents asubstituted or unsubstituted phenylene group, and wherein a total numberof carbon atoms of R¹ to R⁹ and α is greater than or equal to 6 and lessthan or equal to
 16. 15. The compound according to claim 11, wherein thecompound is represented by a general formula (G6),

wherein α represents a substituted or unsubstituted phenylene group,wherein R⁵ represents any of hydrogen, an alkyl group having 1 to 4carbon atoms, and an aryl group having 6 to 10 carbon atoms, and whereina total number of carbon atoms of R⁵ and α is greater than or equal to 6and less than or equal to
 16. 16. The compound according to claim 11,wherein the compound is represented by a general formula (G7),

wherein α represents a substituted or unsubstituted phenylene group,wherein R⁵ represents any of hydrogen, an alkyl group having 1 to 4carbon atoms, and an aryl group having 6 to 10 carbon atoms, and whereina total number of carbon atoms of R⁵ and α is greater than or equal to 6and less than or equal to
 16. 17. The compound according to claim 11,wherein the compound is represented by a structural formula (100),


18. The compound according to claim 11, the compound is represented by astructural formula (127),


19. A light-emitting element comprising: a first electrode; alight-emitting layer over the first electrode; and a second electrodeover the light-emitting layer, wherein the light-emitting layercomprises the compound according to claim
 11. 20. A lighting devicecomprising the light-emitting element according to claim
 19. 21. Adisplay device comprising the light-emitting element according to claim19.